Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $209.55   8.332%   $227.0097   $227.01   $227.00   $227.00  
  Purchase #2 $174.73   13.796%   $198.8358   $198.84   $198.85   $198.80  
  Purchase #3 $203.30   11.120%   $225.907   $225.91   $225.90   $225.90  
  Purchase #4 $156.48   8.773%   $170.208   $170.21   $170.20   $170.20  
  Purchase #5 $105.41   8.215%   $114.0694   $114.07   $114.05   $114.10  
  Purchase #6 $221.93   7.427%   $238.4127   $238.41   $238.40   $238.40  
  Purchase #7 $100.59   6.729%   $107.3587   $107.36   $107.35   $107.40  
  7 purchase totals = $1,171.99       $1,281.8013   $1,281.81   $1,281.75   $1,281.80