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 $75.82   13.146%   $85.7873   $85.79   $85.80   $85.80  
  Purchase #2 $225.70   12.378%   $253.6371   $253.64   $253.65   $253.60  
  Purchase #3 $71.67   9.654%   $78.589   $78.59   $78.60   $78.60  
  Purchase #4 $173.99   13.335%   $197.1916   $197.19   $197.20   $197.20  
  Purchase #5 $126.72   13.158%   $143.3938   $143.39   $143.40   $143.40  
  Purchase #6 $180.51   8.138%   $195.1999   $195.20   $195.20   $195.20  
  Purchase #7 $111.60   7.445%   $119.9086   $119.91   $119.90   $119.90  
  7 purchase totals = $966.01       $1,073.7073   $1,073.71   $1,073.75   $1,073.70