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 $62.58   9.213%   $68.3455   $68.35   $68.35   $68.30  
  Purchase #2 $199.83   5.246%   $210.3131   $210.31   $210.30   $210.30  
  Purchase #3 $127.60   6.400%   $135.7664   $135.77   $135.75   $135.80  
  Purchase #4 $37.72   9.187%   $41.1853   $41.19   $41.20   $41.20  
  Purchase #5 $58.73   3.363%   $60.7051   $60.71   $60.70   $60.70  
  Purchase #6 $46.46   6.731%   $49.5872   $49.59   $49.60   $49.60  
  Purchase #7 $244.36   6.391%   $259.977   $259.98   $260.00   $260.00  
  7 purchase totals = $777.28       $825.8796   $825.90   $825.90   $825.90