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 $6.26   12.276%   $7.0285   $7.03   $7.05   $7.00  
  Purchase #2 $157.65   4.240%   $164.3344   $164.33   $164.35   $164.30  
  Purchase #3 $43.98   11.268%   $48.9357   $48.94   $48.95   $48.90  
  Purchase #4 $113.39   3.390%   $117.2339   $117.23   $117.25   $117.20  
  Purchase #5 $177.78   13.439%   $201.6719   $201.67   $201.65   $201.70  
  Purchase #6 $181.76   4.216%   $189.423   $189.42   $189.40   $189.40  
  Purchase #7 $82.59   13.837%   $94.018   $94.02   $94.00   $94.00  
  7 purchase totals = $763.41       $822.6454   $822.64   $822.65   $822.50