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 $76.27   8.284%   $82.5882   $82.59   $82.60   $82.60  
  Purchase #2 $132.72   12.675%   $149.5423   $149.54   $149.55   $149.50  
  Purchase #3 $183.89   10.265%   $202.7663   $202.77   $202.75   $202.80  
  Purchase #4 $154.75   13.315%   $175.355   $175.36   $175.35   $175.40  
  Purchase #5 $43.40   12.449%   $48.8029   $48.80   $48.80   $48.80  
  Purchase #6 $33.75   11.526%   $37.64   $37.64   $37.65   $37.60  
  Purchase #7 $37.30   10.515%   $41.2221   $41.22   $41.20   $41.20  
  7 purchase totals = $662.08       $737.9168   $737.92   $737.90   $737.90