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 $47.89   11.866%   $53.5726   $53.57   $53.55   $53.60  
  Purchase #2 $81.29   7.276%   $87.2047   $87.20   $87.20   $87.20  
  Purchase #3 $98.94   3.635%   $102.5365   $102.54   $102.55   $102.50  
  Purchase #4 $99.76   8.431%   $108.1708   $108.17   $108.15   $108.20  
  Purchase #5 $227.28   10.460%   $251.0535   $251.05   $251.05   $251.10  
  Purchase #6 $92.65   4.704%   $97.0083   $97.01   $97.00   $97.00  
  Purchase #7 $56.61   11.595%   $63.1739   $63.17   $63.15   $63.20  
  7 purchase totals = $704.42       $762.7203   $762.71   $762.65   $762.80