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 $197.51   11.146%   $219.5245   $219.52   $219.50   $219.50  
  Purchase #2 $61.97   10.119%   $68.2407   $68.24   $68.25   $68.20  
  Purchase #3 $250.99   3.616%   $260.0658   $260.07   $260.05   $260.10  
  Purchase #4 $228.73   3.389%   $236.4817   $236.48   $236.50   $236.50  
  Purchase #5 $228.54   4.871%   $239.6722   $239.67   $239.65   $239.70  
  Purchase #6 $130.57   5.736%   $138.0595   $138.06   $138.05   $138.10  
  Purchase #7 $232.71   3.175%   $240.0985   $240.10   $240.10   $240.10  
  7 purchase totals = $1,331.02       $1,402.1429   $1,402.14   $1,402.10   $1,402.20