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 $111.73   11.655%   $124.7521   $124.75   $124.75   $124.80  
  Purchase #2 $17.81   7.562%   $19.1568   $19.16   $19.15   $19.20  
  Purchase #3 $28.27   13.115%   $31.9776   $31.98   $32.00   $32.00  
  Purchase #4 $98.61   6.276%   $104.7988   $104.80   $104.80   $104.80  
  Purchase #5 $213.90   9.232%   $233.6472   $233.65   $233.65   $233.60  
  Purchase #6 $116.35   13.605%   $132.1794   $132.18   $132.20   $132.20  
  Purchase #7 $220.67   13.188%   $249.772   $249.77   $249.75   $249.80  
  7 purchase totals = $807.34       $896.2839   $896.29   $896.30   $896.40