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 $245.98   7.538%   $264.522   $264.52   $264.50   $264.50  
  Purchase #2 $58.33   12.729%   $65.7548   $65.75   $65.75   $65.80  
  Purchase #3 $175.40   10.663%   $194.1029   $194.10   $194.10   $194.10  
  Purchase #4 $93.50   9.832%   $102.6929   $102.69   $102.70   $102.70  
  Purchase #5 $185.81   9.482%   $203.4285   $203.43   $203.45   $203.40  
  Purchase #6 $56.45   11.204%   $62.7747   $62.77   $62.75   $62.80  
  Purchase #7 $52.42   11.846%   $58.6297   $58.63   $58.65   $58.60  
  7 purchase totals = $867.89       $951.9055   $951.89   $951.90   $951.90