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   11.754%   $194.9996   $195.00   $195.00   $195.00  
  Purchase #2 $210.75   3.849%   $218.8618   $218.86   $218.85   $218.90  
  Purchase #3 $159.30   9.497%   $174.4287   $174.43   $174.45   $174.40  
  Purchase #4 $75.43   8.734%   $82.0181   $82.02   $82.00   $82.00  
  Purchase #5 $15.69   12.340%   $17.6261   $17.63   $17.65   $17.60  
  Purchase #6 $248.98   12.201%   $279.358   $279.36   $279.35   $279.40  
  Purchase #7 $98.73   13.240%   $111.8019   $111.80   $111.80   $111.80  
  7 purchase totals = $983.37       $1,079.0942   $1,079.10   $1,079.10   $1,079.10