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 $62.78   8.738%   $68.2657   $68.27   $68.25   $68.30  
  Purchase #2 $199.35   13.636%   $226.5334   $226.53   $226.55   $226.50  
  Purchase #3 $212.87   3.253%   $219.7947   $219.79   $219.80   $219.80  
  Purchase #4 $18.47   4.831%   $19.3623   $19.36   $19.35   $19.40  
  Purchase #5 $173.53   10.763%   $192.207   $192.21   $192.20   $192.20  
  Purchase #6 $47.30   6.764%   $50.4994   $50.50   $50.50   $50.50  
  Purchase #7 $76.38   10.707%   $84.558   $84.56   $84.55   $84.60  
  7 purchase totals = $790.68       $861.2205   $861.22   $861.20   $861.30