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 $189.93   4.654%   $198.7693   $198.77   $198.75   $198.80  
  Purchase #2 $192.76   8.791%   $209.7055   $209.71   $209.70   $209.70  
  Purchase #3 $173.62   11.515%   $193.6123   $193.61   $193.60   $193.60  
  Purchase #4 $54.51   9.460%   $59.6666   $59.67   $59.65   $59.70  
  Purchase #5 $123.73   13.475%   $140.4026   $140.40   $140.40   $140.40  
  Purchase #6 $249.65   7.390%   $268.0991   $268.10   $268.10   $268.10  
  Purchase #7 $227.76   11.654%   $254.3032   $254.30   $254.30   $254.30  
  7 purchase totals = $1,211.96       $1,324.5586   $1,324.56   $1,324.50   $1,324.60