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 $119.98   4.868%   $125.8206   $125.82   $125.80   $125.80  
  Purchase #2 $178.42   13.801%   $203.0437   $203.04   $203.05   $203.00  
  Purchase #3 $237.43   7.473%   $255.1731   $255.17   $255.15   $255.20  
  Purchase #4 $175.54   10.572%   $194.0981   $194.10   $194.10   $194.10  
  Purchase #5 $89.87   5.157%   $94.5046   $94.50   $94.50   $94.50  
  Purchase #6 $172.38   13.577%   $195.784   $195.78   $195.80   $195.80  
  Purchase #7 $86.34   6.692%   $92.1179   $92.12   $92.10   $92.10  
  7 purchase totals = $1,059.96       $1,160.5420   $1,160.53   $1,160.50   $1,160.50