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 $245.27   3.707%   $254.3622   $254.36   $254.35   $254.40  
  Purchase #2 $91.62   5.494%   $96.6536   $96.65   $96.65   $96.70  
  Purchase #3 $165.95   10.224%   $182.9167   $182.92   $182.90   $182.90  
  Purchase #4 $16.54   9.508%   $18.1126   $18.11   $18.10   $18.10  
  Purchase #5 $63.37   4.624%   $66.3002   $66.30   $66.30   $66.30  
  Purchase #6 $188.91   3.332%   $195.2045   $195.20   $195.20   $195.20  
  Purchase #7 $52.37   6.308%   $55.6735   $55.67   $55.65   $55.70  
  7 purchase totals = $824.03       $869.2233   $869.21   $869.15   $869.30