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 $86.54   12.731%   $97.5574   $97.56   $97.55   $97.60  
  Purchase #2 $77.80   8.559%   $84.4589   $84.46   $84.45   $84.50  
  Purchase #3 $46.65   9.293%   $50.9852   $50.99   $51.00   $51.00  
  Purchase #4 $111.75   11.596%   $124.7085   $124.71   $124.70   $124.70  
  Purchase #5 $8.96   10.744%   $9.9227   $9.92   $9.90   $9.90  
  Purchase #6 $246.99   7.347%   $265.1364   $265.14   $265.15   $265.10  
  Purchase #7 $246.49   6.507%   $262.5291   $262.53   $262.55   $262.50  
  7 purchase totals = $825.18       $895.2982   $895.31   $895.30   $895.30