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 $29.88   12.323%   $33.5621   $33.56   $33.55   $33.60  
  Purchase #2 $161.91   9.873%   $177.8954   $177.90   $177.90   $177.90  
  Purchase #3 $119.35   13.645%   $135.6353   $135.64   $135.65   $135.60  
  Purchase #4 $44.25   10.259%   $48.7896   $48.79   $48.80   $48.80  
  Purchase #5 $158.73   12.516%   $178.5966   $178.60   $178.60   $178.60  
  Purchase #6 $99.50   6.607%   $106.074   $106.07   $106.05   $106.10  
  Purchase #7 $49.82   9.866%   $54.7352   $54.74   $54.75   $54.70  
  7 purchase totals = $663.44       $735.2882   $735.30   $735.30   $735.30