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 $140.84   11.292%   $156.7437   $156.74   $156.75   $156.70  
  Purchase #2 $232.57   4.163%   $242.2519   $242.25   $242.25   $242.30  
  Purchase #3 $179.33   6.362%   $190.739   $190.74   $190.75   $190.70  
  Purchase #4 $93.71   11.267%   $104.2683   $104.27   $104.25   $104.30  
  Purchase #5 $25.75   10.337%   $28.4118   $28.41   $28.40   $28.40  
  Purchase #6 $74.63   10.494%   $82.4617   $82.46   $82.45   $82.50  
  Purchase #7 $158.97   5.457%   $167.645   $167.65   $167.65   $167.60  
  7 purchase totals = $905.80       $972.5214   $972.52   $972.50   $972.50