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 $153.79   8.316%   $166.5792   $166.58   $166.60   $166.60  
  Purchase #2 $195.44   3.790%   $202.8472   $202.85   $202.85   $202.80  
  Purchase #3 $44.60   10.606%   $49.3303   $49.33   $49.35   $49.30  
  Purchase #4 $61.45   9.299%   $67.1642   $67.16   $67.15   $67.20  
  Purchase #5 $131.33   12.770%   $148.1008   $148.10   $148.10   $148.10  
  Purchase #6 $94.84   8.825%   $103.2096   $103.21   $103.20   $103.20  
  Purchase #7 $44.76   4.109%   $46.5992   $46.60   $46.60   $46.60  
  7 purchase totals = $726.21       $783.8305   $783.83   $783.85   $783.80