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 $54.54   8.736%   $59.3046   $59.30   $59.30   $59.30  
  Purchase #2 $186.50   9.642%   $204.4823   $204.48   $204.50   $204.50  
  Purchase #3 $149.70   7.461%   $160.8691   $160.87   $160.85   $160.90  
  Purchase #4 $64.58   3.388%   $66.768   $66.77   $66.75   $66.80  
  Purchase #5 $40.36   12.431%   $45.3772   $45.38   $45.40   $45.40  
  Purchase #6 $244.75   6.507%   $260.6759   $260.68   $260.70   $260.70  
  Purchase #7 $85.61   10.525%   $94.6205   $94.62   $94.60   $94.60  
  7 purchase totals = $826.04       $892.0976   $892.10   $892.10   $892.20