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 $45.63   13.305%   $51.7011   $51.70   $51.70   $51.70  
  Purchase #2 $208.69   4.749%   $218.6007   $218.60   $218.60   $218.60  
  Purchase #3 $100.33   4.249%   $104.593   $104.59   $104.60   $104.60  
  Purchase #4 $36.65   7.570%   $39.4244   $39.42   $39.40   $39.40  
  Purchase #5 $168.41   3.648%   $174.5536   $174.55   $174.55   $174.60  
  Purchase #6 $67.81   4.271%   $70.7062   $70.71   $70.70   $70.70  
  Purchase #7 $152.66   7.104%   $163.505   $163.51   $163.50   $163.50  
  7 purchase totals = $780.18       $823.0840   $823.08   $823.05   $823.10