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 $236.26   9.754%   $259.3048   $259.30   $259.30   $259.30  
  Purchase #2 $46.59   4.241%   $48.5659   $48.57   $48.55   $48.60  
  Purchase #3 $56.46   12.147%   $63.3182   $63.32   $63.30   $63.30  
  Purchase #4 $56.28   7.616%   $60.5663   $60.57   $60.55   $60.60  
  Purchase #5 $97.25   7.107%   $104.1616   $104.16   $104.15   $104.20  
  Purchase #6 $225.96   8.393%   $244.9248   $244.92   $244.90   $244.90  
  Purchase #7 $39.87   11.747%   $44.5535   $44.55   $44.55   $44.60  
  7 purchase totals = $758.67       $825.3951   $825.39   $825.30   $825.50