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 $68.96   11.604%   $76.9621   $76.96   $76.95   $77.00  
  Purchase #2 $9.95   6.787%   $10.6253   $10.63   $10.65   $10.60  
  Purchase #3 $101.78   4.651%   $106.5138   $106.51   $106.50   $106.50  
  Purchase #4 $91.88   8.831%   $99.9939   $99.99   $100.00   $100.00  
  Purchase #5 $244.60   5.793%   $258.7697   $258.77   $258.75   $258.80  
  Purchase #6 $161.81   6.650%   $172.5704   $172.57   $172.55   $172.60  
  Purchase #7 $62.71   10.659%   $69.3943   $69.39   $69.40   $69.40  
  7 purchase totals = $741.69       $794.8295   $794.82   $794.80   $794.90