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 $180.35   8.110%   $194.9764   $194.98   $195.00   $195.00  
  Purchase #2 $180.88   6.343%   $192.3532   $192.35   $192.35   $192.40  
  Purchase #3 $220.70   10.517%   $243.911   $243.91   $243.90   $243.90  
  Purchase #4 $232.28   5.589%   $245.2621   $245.26   $245.25   $245.30  
  Purchase #5 $205.92   4.463%   $215.1102   $215.11   $215.10   $215.10  
  Purchase #6 $6.39   5.762%   $6.7582   $6.76   $6.75   $6.80  
  Purchase #7 $118.32   7.470%   $127.1585   $127.16   $127.15   $127.20  
  7 purchase totals = $1,144.84       $1,225.5296   $1,225.53   $1,225.50   $1,225.70