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 $111.27   13.559%   $126.3571   $126.36   $126.35   $126.40  
  Purchase #2 $15.74   5.325%   $16.5782   $16.58   $16.60   $16.60  
  Purchase #3 $71.28   6.846%   $76.1598   $76.16   $76.15   $76.20  
  Purchase #4 $45.90   12.560%   $51.665   $51.67   $51.65   $51.70  
  Purchase #5 $176.67   5.401%   $186.2119   $186.21   $186.20   $186.20  
  Purchase #6 $59.33   5.757%   $62.7456   $62.75   $62.75   $62.70  
  Purchase #7 $219.38   3.450%   $226.9486   $226.95   $226.95   $226.90  
  7 purchase totals = $699.57       $746.6662   $746.68   $746.65   $746.70