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 $56.76   4.129%   $59.1036   $59.10   $59.10   $59.10  
  Purchase #2 $214.25   8.334%   $232.1056   $232.11   $232.10   $232.10  
  Purchase #3 $94.76   8.187%   $102.518   $102.52   $102.50   $102.50  
  Purchase #4 $65.62   4.214%   $68.3852   $68.39   $68.40   $68.40  
  Purchase #5 $55.50   12.329%   $62.3426   $62.34   $62.35   $62.30  
  Purchase #6 $56.49   4.147%   $58.8326   $58.83   $58.85   $58.80  
  Purchase #7 $147.93   10.356%   $163.2496   $163.25   $163.25   $163.20  
  7 purchase totals = $691.31       $746.5372   $746.54   $746.55   $746.40