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 $229.39   8.752%   $249.4662   $249.47   $249.45   $249.50  
  Purchase #2 $164.74   12.201%   $184.8399   $184.84   $184.85   $184.80  
  Purchase #3 $184.84   9.138%   $201.7307   $201.73   $201.75   $201.70  
  Purchase #4 $102.52   3.333%   $105.937   $105.94   $105.95   $105.90  
  Purchase #5 $201.46   11.441%   $224.509   $224.51   $224.50   $224.50  
  Purchase #6 $205.53   5.774%   $217.3973   $217.40   $217.40   $217.40  
  Purchase #7 $58.88   3.507%   $60.9449   $60.94   $60.95   $60.90  
  7 purchase totals = $1,147.36       $1,244.8250   $1,244.83   $1,244.85   $1,244.70