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 $98.86   5.217%   $104.0175   $104.02   $104.00   $104.00  
  Purchase #2 $90.82   5.247%   $95.5853   $95.59   $95.60   $95.60  
  Purchase #3 $67.44   8.664%   $73.283   $73.28   $73.30   $73.30  
  Purchase #4 $122.58   3.503%   $126.874   $126.87   $126.85   $126.90  
  Purchase #5 $245.68   4.212%   $256.028   $256.03   $256.05   $256.00  
  Purchase #6 $77.79   7.561%   $83.6717   $83.67   $83.65   $83.70  
  Purchase #7 $182.34   3.122%   $188.0327   $188.03   $188.05   $188.00  
  7 purchase totals = $885.51       $927.4922   $927.49   $927.50   $927.50