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 $94.53   7.874%   $101.9733   $101.97   $101.95   $102.00  
  Purchase #2 $152.25   4.603%   $159.2581   $159.26   $159.25   $159.30  
  Purchase #3 $76.68   3.456%   $79.3301   $79.33   $79.35   $79.30  
  Purchase #4 $231.88   4.184%   $241.5819   $241.58   $241.60   $241.60  
  Purchase #5 $46.74   12.768%   $52.7078   $52.71   $52.70   $52.70  
  Purchase #6 $116.26   11.366%   $129.4741   $129.47   $129.45   $129.50  
  Purchase #7 $92.81   11.255%   $103.2558   $103.26   $103.25   $103.30  
  7 purchase totals = $811.15       $867.5811   $867.58   $867.55   $867.70