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 $124.85   12.408%   $140.3414   $140.34   $140.35   $140.30  
  Purchase #2 $250.47   6.706%   $267.2665   $267.27   $267.25   $267.30  
  Purchase #3 $193.94   5.644%   $204.886   $204.89   $204.90   $204.90  
  Purchase #4 $163.96   8.206%   $177.4146   $177.41   $177.40   $177.40  
  Purchase #5 $215.34   4.181%   $224.3434   $224.34   $224.35   $224.30  
  Purchase #6 $241.25   5.253%   $253.9229   $253.92   $253.90   $253.90  
  Purchase #7 $78.42   13.561%   $89.0545   $89.05   $89.05   $89.10  
  7 purchase totals = $1,268.23       $1,357.2293   $1,357.22   $1,357.20   $1,357.20