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 $46.94   7.810%   $50.606   $50.61   $50.60   $50.60  
  Purchase #2 $5.33   11.318%   $5.9332   $5.93   $5.95   $5.90  
  Purchase #3 $27.99   4.441%   $29.233   $29.23   $29.25   $29.20  
  Purchase #4 $59.75   4.258%   $62.2942   $62.29   $62.30   $62.30  
  Purchase #5 $63.78   10.153%   $70.2556   $70.26   $70.25   $70.30  
  Purchase #6 $68.65   10.664%   $75.9708   $75.97   $75.95   $76.00  
  Purchase #7 $38.61   10.352%   $42.6069   $42.61   $42.60   $42.60  
  7 purchase totals = $311.05       $336.8997   $336.90   $336.90   $336.90