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 $208.81   11.852%   $233.5582   $233.56   $233.55   $233.60  
  Purchase #2 $172.90   12.639%   $194.7528   $194.75   $194.75   $194.80  
  Purchase #3 $225.28   8.623%   $244.7059   $244.71   $244.70   $244.70  
  Purchase #4 $130.78   5.123%   $137.4799   $137.48   $137.50   $137.50  
  Purchase #5 $163.37   3.108%   $168.4475   $168.45   $168.45   $168.40  
  Purchase #6 $205.26   4.752%   $215.014   $215.01   $215.00   $215.00  
  Purchase #7 $98.34   6.558%   $104.7891   $104.79   $104.80   $104.80  
  7 purchase totals = $1,204.74       $1,298.7474   $1,298.75   $1,298.75   $1,298.80