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 $57.25   11.808%   $64.0101   $64.01   $64.00   $64.00  
  Purchase #2 $113.78   11.473%   $126.834   $126.83   $126.85   $126.80  
  Purchase #3 $210.77   3.874%   $218.9352   $218.94   $218.95   $218.90  
  Purchase #4 $242.47   4.838%   $254.2007   $254.20   $254.20   $254.20  
  Purchase #5 $162.31   5.361%   $171.0114   $171.01   $171.00   $171.00  
  Purchase #6 $208.65   9.505%   $228.4822   $228.48   $228.50   $228.50  
  Purchase #7 $239.41   3.390%   $247.526   $247.53   $247.55   $247.50  
  7 purchase totals = $1,234.64       $1,310.9996   $1,311.00   $1,311.05   $1,310.90