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 $59.76   5.673%   $63.1502   $63.15   $63.15   $63.20  
  Purchase #2 $182.82   13.471%   $207.4477   $207.45   $207.45   $207.40  
  Purchase #3 $75.94   11.695%   $84.8212   $84.82   $84.80   $84.80  
  Purchase #4 $232.62   5.800%   $246.112   $246.11   $246.10   $246.10  
  Purchase #5 $76.97   7.216%   $82.5242   $82.52   $82.50   $82.50  
  Purchase #6 $32.87   5.360%   $34.6318   $34.63   $34.65   $34.60  
  Purchase #7 $161.75   10.219%   $178.2792   $178.28   $178.30   $178.30  
  7 purchase totals = $822.73       $896.9663   $896.96   $896.95   $896.90