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 $215.51   6.112%   $228.682   $228.68   $228.70   $228.70  
  Purchase #2 $183.81   12.504%   $206.7936   $206.79   $206.80   $206.80  
  Purchase #3 $19.37   9.156%   $21.1435   $21.14   $21.15   $21.10  
  Purchase #4 $41.77   10.763%   $46.2657   $46.27   $46.25   $46.30  
  Purchase #5 $11.93   13.204%   $13.5052   $13.51   $13.50   $13.50  
  Purchase #6 $240.98   3.632%   $249.7324   $249.73   $249.75   $249.70  
  Purchase #7 $228.79   8.486%   $248.2051   $248.21   $248.20   $248.20  
  7 purchase totals = $942.16       $1,014.3275   $1,014.33   $1,014.35   $1,014.30