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 $10.38   11.754%   $11.6001   $11.60   $11.60   $11.60  
  Purchase #2 $232.39   4.826%   $243.6051   $243.61   $243.60   $243.60  
  Purchase #3 $39.54   8.604%   $42.942   $42.94   $42.95   $42.90  
  Purchase #4 $218.86   5.727%   $231.3941   $231.39   $231.40   $231.40  
  Purchase #5 $125.91   8.438%   $136.5343   $136.53   $136.55   $136.50  
  Purchase #6 $59.32   8.110%   $64.1309   $64.13   $64.15   $64.10  
  Purchase #7 $106.43   8.705%   $115.6947   $115.69   $115.70   $115.70  
  7 purchase totals = $792.83       $845.9012   $845.89   $845.95   $845.80