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 $174.49   11.753%   $194.9978   $195.00   $195.00   $195.00  
  Purchase #2 $211.63   7.760%   $228.0525   $228.05   $228.05   $228.10  
  Purchase #3 $29.96   3.667%   $31.0586   $31.06   $31.05   $31.10  
  Purchase #4 $225.41   11.206%   $250.6694   $250.67   $250.65   $250.70  
  Purchase #5 $192.76   11.409%   $214.752   $214.75   $214.75   $214.80  
  Purchase #6 $197.76   9.662%   $216.8676   $216.87   $216.85   $216.90  
  Purchase #7 $109.80   9.238%   $119.9433   $119.94   $119.95   $119.90  
  7 purchase totals = $1,141.81       $1,256.3412   $1,256.34   $1,256.30   $1,256.50