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 $52.53   6.621%   $56.008   $56.01   $56.00   $56.00  
  Purchase #2 $164.89   7.186%   $176.739   $176.74   $176.75   $176.70  
  Purchase #3 $185.86   13.441%   $210.8414   $210.84   $210.85   $210.80  
  Purchase #4 $133.79   6.583%   $142.5974   $142.60   $142.60   $142.60  
  Purchase #5 $86.81   6.832%   $92.7409   $92.74   $92.75   $92.70  
  Purchase #6 $171.46   9.713%   $188.1139   $188.11   $188.10   $188.10  
  Purchase #7 $174.96   6.677%   $186.6421   $186.64   $186.65   $186.60  
  7 purchase totals = $970.30       $1,053.6827   $1,053.68   $1,053.70   $1,053.50