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 $201.47   7.730%   $217.0436   $217.04   $217.05   $217.00  
  Purchase #2 $103.50   13.266%   $117.2303   $117.23   $117.25   $117.20  
  Purchase #3 $38.34   10.245%   $42.2679   $42.27   $42.25   $42.30  
  Purchase #4 $75.99   10.536%   $83.9963   $84.00   $84.00   $84.00  
  Purchase #5 $192.65   8.718%   $209.4452   $209.45   $209.45   $209.40  
  Purchase #6 $231.53   3.258%   $239.0732   $239.07   $239.05   $239.10  
  Purchase #7 $140.91   7.313%   $151.2147   $151.21   $151.20   $151.20  
  7 purchase totals = $984.39       $1,060.2712   $1,060.27   $1,060.25   $1,060.20