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 $213.66   8.715%   $232.2805   $232.28   $232.30   $232.30  
  Purchase #2 $214.28   11.634%   $239.2093   $239.21   $239.20   $239.20  
  Purchase #3 $65.91   11.588%   $73.5477   $73.55   $73.55   $73.50  
  Purchase #4 $231.81   11.620%   $258.7463   $258.75   $258.75   $258.70  
  Purchase #5 $25.97   13.834%   $29.5627   $29.56   $29.55   $29.60  
  Purchase #6 $196.25   6.233%   $208.4823   $208.48   $208.50   $208.50  
  Purchase #7 $222.49   8.762%   $241.9846   $241.98   $242.00   $242.00  
  7 purchase totals = $1,170.37       $1,283.8134   $1,283.81   $1,283.85   $1,283.80