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 $88.68   4.620%   $92.777   $92.78   $92.80   $92.80  
  Purchase #2 $61.45   8.314%   $66.559   $66.56   $66.55   $66.60  
  Purchase #3 $117.34   12.774%   $132.329   $132.33   $132.35   $132.30  
  Purchase #4 $118.94   7.622%   $128.0056   $128.01   $128.00   $128.00  
  Purchase #5 $120.26   8.853%   $130.9066   $130.91   $130.90   $130.90  
  Purchase #6 $199.78   10.439%   $220.635   $220.64   $220.65   $220.60  
  Purchase #7 $161.96   13.841%   $184.3769   $184.38   $184.40   $184.40  
  7 purchase totals = $868.41       $955.5891   $955.61   $955.65   $955.60