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 $118.56   12.791%   $133.725   $133.73   $133.75   $133.70  
  Purchase #2 $43.60   10.691%   $48.2613   $48.26   $48.25   $48.30  
  Purchase #3 $174.87   7.766%   $188.4504   $188.45   $188.45   $188.50  
  Purchase #4 $159.28   3.121%   $164.2511   $164.25   $164.25   $164.30  
  Purchase #5 $226.36   11.718%   $252.8849   $252.88   $252.90   $252.90  
  Purchase #6 $168.30   13.793%   $191.5136   $191.51   $191.50   $191.50  
  Purchase #7 $64.47   3.304%   $66.6001   $66.60   $66.60   $66.60  
  7 purchase totals = $955.44       $1,045.6864   $1,045.68   $1,045.70   $1,045.80