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 $60.98   7.392%   $65.4876   $65.49   $65.50   $65.50  
  Purchase #2 $195.36   4.136%   $203.4401   $203.44   $203.45   $203.40  
  Purchase #3 $154.32   6.152%   $163.8138   $163.81   $163.80   $163.80  
  Purchase #4 $20.82   3.802%   $21.6116   $21.61   $21.60   $21.60  
  Purchase #5 $172.69   6.260%   $183.5004   $183.50   $183.50   $183.50  
  Purchase #6 $232.26   5.108%   $244.1238   $244.12   $244.10   $244.10  
  Purchase #7 $47.59   4.525%   $49.7434   $49.74   $49.75   $49.70  
  7 purchase totals = $884.02       $931.7207   $931.71   $931.70   $931.60