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 $202.73   10.832%   $224.6897   $224.69   $224.70   $224.70  
  Purchase #2 $66.36   10.119%   $73.075   $73.08   $73.10   $73.10  
  Purchase #3 $108.71   7.359%   $116.71   $116.71   $116.70   $116.70  
  Purchase #4 $43.54   5.652%   $46.0009   $46.00   $46.00   $46.00  
  Purchase #5 $21.68   9.598%   $23.7608   $23.76   $23.75   $23.80  
  Purchase #6 $156.85   9.151%   $171.2033   $171.20   $171.20   $171.20  
  Purchase #7 $96.66   8.461%   $104.8384   $104.84   $104.85   $104.80  
  7 purchase totals = $696.53       $760.2781   $760.28   $760.30   $760.30