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 $208.82   13.368%   $236.7351   $236.74   $236.75   $236.70  
  Purchase #2 $30.71   10.757%   $34.0135   $34.01   $34.00   $34.00  
  Purchase #3 $152.95   4.349%   $159.6018   $159.60   $159.60   $159.60  
  Purchase #4 $134.25   6.640%   $143.1642   $143.16   $143.15   $143.20  
  Purchase #5 $30.75   3.614%   $31.8613   $31.86   $31.85   $31.90  
  Purchase #6 $199.80   7.207%   $214.1996   $214.20   $214.20   $214.20  
  Purchase #7 $153.47   13.702%   $174.4985   $174.50   $174.50   $174.50  
  7 purchase totals = $910.75       $994.0740   $994.07   $994.05   $994.10