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 $92.29   6.683%   $98.4577   $98.46   $98.45   $98.50  
  Purchase #2 $42.44   10.178%   $46.7595   $46.76   $46.75   $46.80  
  Purchase #3 $159.70   8.587%   $173.4134   $173.41   $173.40   $173.40  
  Purchase #4 $79.44   11.768%   $88.7885   $88.79   $88.80   $88.80  
  Purchase #5 $182.57   5.215%   $192.091   $192.09   $192.10   $192.10  
  Purchase #6 $67.77   4.863%   $71.0657   $71.07   $71.05   $71.10  
  Purchase #7 $31.27   10.581%   $34.5787   $34.58   $34.60   $34.60  
  7 purchase totals = $655.48       $705.1545   $705.16   $705.15   $705.30