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 $165.26   11.468%   $184.212   $184.21   $184.20   $184.20  
  Purchase #2 $173.79   10.847%   $192.641   $192.64   $192.65   $192.60  
  Purchase #3 $197.95   10.833%   $219.3939   $219.39   $219.40   $219.40  
  Purchase #4 $55.26   4.275%   $57.6224   $57.62   $57.60   $57.60  
  Purchase #5 $177.48   4.370%   $185.2359   $185.24   $185.25   $185.20  
  Purchase #6 $72.91   9.186%   $79.6075   $79.61   $79.60   $79.60  
  Purchase #7 $39.67   4.854%   $41.5956   $41.60   $41.60   $41.60  
  7 purchase totals = $882.32       $960.3083   $960.31   $960.30   $960.20