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 $56.42   11.601%   $62.9653   $62.97   $62.95   $63.00  
  Purchase #2 $11.59   13.329%   $13.1348   $13.13   $13.15   $13.10  
  Purchase #3 $16.53   8.366%   $17.9129   $17.91   $17.90   $17.90  
  Purchase #4 $23.48   4.347%   $24.5007   $24.50   $24.50   $24.50  
  Purchase #5 $11.99   7.722%   $12.9159   $12.92   $12.90   $12.90  
  Purchase #6 $143.75   4.363%   $150.0218   $150.02   $150.00   $150.00  
  Purchase #7 $48.66   13.107%   $55.0379   $55.04   $55.05   $55.00  
  7 purchase totals = $312.42       $336.4893   $336.49   $336.45   $336.40