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 $175.82   9.186%   $191.9708   $191.97   $191.95   $192.00  
  Purchase #2 $73.68   13.374%   $83.534   $83.53   $83.55   $83.50  
  Purchase #3 $120.29   11.574%   $134.2124   $134.21   $134.20   $134.20  
  Purchase #4 $224.72   8.103%   $242.9291   $242.93   $242.95   $242.90  
  Purchase #5 $233.54   11.480%   $260.3504   $260.35   $260.35   $260.40  
  Purchase #6 $180.27   6.248%   $191.5333   $191.53   $191.55   $191.50  
  Purchase #7 $10.73   4.867%   $11.2522   $11.25   $11.25   $11.30  
  7 purchase totals = $1,019.05       $1,115.7822   $1,115.77   $1,115.80   $1,115.80