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 $85.45   8.545%   $92.7517   $92.75   $92.75   $92.80  
  Purchase #2 $155.75   13.828%   $177.2871   $177.29   $177.30   $177.30  
  Purchase #3 $63.84   10.440%   $70.5049   $70.50   $70.50   $70.50  
  Purchase #4 $112.52   6.707%   $120.0667   $120.07   $120.05   $120.10  
  Purchase #5 $222.38   10.131%   $244.9093   $244.91   $244.90   $244.90  
  Purchase #6 $184.26   6.635%   $196.4857   $196.49   $196.50   $196.50  
  Purchase #7 $112.50   6.338%   $119.6303   $119.63   $119.65   $119.60  
  7 purchase totals = $936.70       $1,021.6357   $1,021.64   $1,021.65   $1,021.70