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 $198.56   3.223%   $204.9596   $204.96   $204.95   $205.00  
  Purchase #2 $244.71   4.779%   $256.4047   $256.40   $256.40   $256.40  
  Purchase #3 $161.53   11.789%   $180.5728   $180.57   $180.55   $180.60  
  Purchase #4 $213.36   13.393%   $241.9353   $241.94   $241.95   $241.90  
  Purchase #5 $136.66   12.250%   $153.4009   $153.40   $153.40   $153.40  
  Purchase #6 $227.44   7.436%   $244.3524   $244.35   $244.35   $244.40  
  Purchase #7 $72.88   10.772%   $80.7306   $80.73   $80.75   $80.70  
  7 purchase totals = $1,255.14       $1,362.3563   $1,362.35   $1,362.35   $1,362.40