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 $245.53   11.191%   $273.0073   $273.01   $273.00   $273.00  
  Purchase #2 $205.42   9.608%   $225.1568   $225.16   $225.15   $225.20  
  Purchase #3 $50.75   6.465%   $54.031   $54.03   $54.05   $54.00  
  Purchase #4 $183.92   8.237%   $199.0695   $199.07   $199.05   $199.10  
  Purchase #5 $119.47   10.165%   $131.6141   $131.61   $131.60   $131.60  
  Purchase #6 $190.82   6.803%   $203.8015   $203.80   $203.80   $203.80  
  Purchase #7 $227.43   5.817%   $240.6596   $240.66   $240.65   $240.70  
  7 purchase totals = $1,223.34       $1,327.3398   $1,327.34   $1,327.30   $1,327.40