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 $219.51   9.796%   $241.0132   $241.01   $241.00   $241.00  
  Purchase #2 $155.77   4.327%   $162.5102   $162.51   $162.50   $162.50  
  Purchase #3 $119.89   10.615%   $132.6163   $132.62   $132.60   $132.60  
  Purchase #4 $138.88   11.628%   $155.029   $155.03   $155.05   $155.00  
  Purchase #5 $184.98   10.302%   $204.0366   $204.04   $204.05   $204.00  
  Purchase #6 $21.79   8.829%   $23.7138   $23.71   $23.70   $23.70  
  Purchase #7 $144.40   9.573%   $158.2234   $158.22   $158.20   $158.20  
  7 purchase totals = $985.22       $1,077.1425   $1,077.14   $1,077.10   $1,077.00