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 $62.68   4.430%   $65.4567   $65.46   $65.45   $65.50  
  Purchase #2 $95.71   5.730%   $101.1942   $101.19   $101.20   $101.20  
  Purchase #3 $174.31   7.377%   $187.1688   $187.17   $187.15   $187.20  
  Purchase #4 $236.98   3.156%   $244.4591   $244.46   $244.45   $244.50  
  Purchase #5 $223.57   3.165%   $230.646   $230.65   $230.65   $230.60  
  Purchase #6 $236.28   8.824%   $257.1293   $257.13   $257.15   $257.10  
  Purchase #7 $179.89   5.352%   $189.5177   $189.52   $189.50   $189.50  
  7 purchase totals = $1,209.42       $1,275.5718   $1,275.58   $1,275.55   $1,275.60