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 $59.40   10.720%   $65.7677   $65.77   $65.75   $65.80  
  Purchase #2 $85.58   10.660%   $94.7028   $94.70   $94.70   $94.70  
  Purchase #3 $75.33   11.709%   $84.1504   $84.15   $84.15   $84.20  
  Purchase #4 $111.34   6.223%   $118.2687   $118.27   $118.25   $118.30  
  Purchase #5 $153.93   11.240%   $171.2317   $171.23   $171.25   $171.20  
  Purchase #6 $132.98   11.661%   $148.4868   $148.49   $148.50   $148.50  
  Purchase #7 $219.34   10.312%   $241.9583   $241.96   $241.95   $242.00  
  7 purchase totals = $837.90       $924.5664   $924.57   $924.55   $924.70