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 $184.47   4.264%   $192.3358   $192.34   $192.35   $192.30  
  Purchase #2 $10.91   13.514%   $12.3844   $12.38   $12.40   $12.40  
  Purchase #3 $180.39   6.457%   $192.0378   $192.04   $192.05   $192.00  
  Purchase #4 $44.61   4.661%   $46.6893   $46.69   $46.70   $46.70  
  Purchase #5 $24.82   4.393%   $25.9103   $25.91   $25.90   $25.90  
  Purchase #6 $162.47   8.607%   $176.4538   $176.45   $176.45   $176.50  
  Purchase #7 $219.73   7.423%   $236.0406   $236.04   $236.05   $236.00  
  7 purchase totals = $827.40       $881.8520   $881.85   $881.90   $881.80