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 $56.46   8.505%   $61.2619   $61.26   $61.25   $61.30  
  Purchase #2 $21.31   12.368%   $23.9456   $23.95   $23.95   $23.90  
  Purchase #3 $105.88   9.596%   $116.0402   $116.04   $116.05   $116.00  
  Purchase #4 $124.86   8.372%   $135.3133   $135.31   $135.30   $135.30  
  Purchase #5 $19.25   6.582%   $20.517   $20.52   $20.50   $20.50  
  Purchase #6 $59.54   5.687%   $62.926   $62.93   $62.95   $62.90  
  Purchase #7 $77.25   11.486%   $86.1229   $86.12   $86.10   $86.10  
  7 purchase totals = $464.55       $506.1269   $506.13   $506.10   $506.00