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 $9.52   4.251%   $9.9247   $9.92   $9.90   $9.90  
  Purchase #2 $124.42   12.122%   $139.5022   $139.50   $139.50   $139.50  
  Purchase #3 $6.52   9.664%   $7.1501   $7.15   $7.15   $7.20  
  Purchase #4 $21.45   6.155%   $22.7702   $22.77   $22.75   $22.80  
  Purchase #5 $241.83   13.722%   $275.0139   $275.01   $275.00   $275.00  
  Purchase #6 $11.87   3.267%   $12.2578   $12.26   $12.25   $12.30  
  Purchase #7 $83.68   10.450%   $92.4246   $92.42   $92.40   $92.40  
  7 purchase totals = $499.29       $559.0435   $559.03   $558.95   $559.10