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 $176.44   8.530%   $191.4903   $191.49   $191.50   $191.50  
  Purchase #2 $81.76   13.204%   $92.5556   $92.56   $92.55   $92.60  
  Purchase #3 $53.31   9.756%   $58.5109   $58.51   $58.50   $58.50  
  Purchase #4 $219.69   9.695%   $240.9889   $240.99   $241.00   $241.00  
  Purchase #5 $7.98   5.334%   $8.4057   $8.41   $8.40   $8.40  
  Purchase #6 $50.43   3.487%   $52.1885   $52.19   $52.20   $52.20  
  Purchase #7 $248.27   4.580%   $259.6408   $259.64   $259.65   $259.60  
  7 purchase totals = $837.88       $903.7807   $903.79   $903.80   $903.80