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 $88.28   7.207%   $94.6423   $94.64   $94.65   $94.60  
  Purchase #2 $27.26   10.733%   $30.1858   $30.19   $30.20   $30.20  
  Purchase #3 $28.32   3.258%   $29.2427   $29.24   $29.25   $29.20  
  Purchase #4 $235.57   5.373%   $248.2272   $248.23   $248.25   $248.20  
  Purchase #5 $110.74   8.824%   $120.5117   $120.51   $120.50   $120.50  
  Purchase #6 $60.68   5.549%   $64.0471   $64.05   $64.05   $64.00  
  Purchase #7 $78.95   6.692%   $84.2333   $84.23   $84.25   $84.20  
  7 purchase totals = $629.80       $671.0901   $671.09   $671.15   $670.90