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 $64.95   6.519%   $69.1841   $69.18   $69.20   $69.20  
  Purchase #2 $238.42   13.365%   $270.2848   $270.28   $270.30   $270.30  
  Purchase #3 $108.65   9.577%   $119.0554   $119.06   $119.05   $119.10  
  Purchase #4 $153.58   13.255%   $173.937   $173.94   $173.95   $173.90  
  Purchase #5 $175.35   12.796%   $197.7878   $197.79   $197.80   $197.80  
  Purchase #6 $52.83   13.296%   $59.8543   $59.85   $59.85   $59.90  
  Purchase #7 $41.38   6.457%   $44.0519   $44.05   $44.05   $44.10  
  7 purchase totals = $835.16       $934.1553   $934.15   $934.20   $934.30