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 $13.65   5.694%   $14.4272   $14.43   $14.45   $14.40  
  Purchase #2 $216.47   5.534%   $228.4494   $228.45   $228.45   $228.40  
  Purchase #3 $165.84   4.291%   $172.9562   $172.96   $172.95   $173.00  
  Purchase #4 $36.25   3.549%   $37.5365   $37.54   $37.55   $37.50  
  Purchase #5 $224.33   7.746%   $241.7066   $241.71   $241.70   $241.70  
  Purchase #6 $151.36   9.105%   $165.1413   $165.14   $165.15   $165.10  
  Purchase #7 $135.73   3.243%   $140.1317   $140.13   $140.15   $140.10  
  7 purchase totals = $943.63       $1,000.3489   $1,000.36   $1,000.40   $1,000.20