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 $61.69   10.574%   $68.2131   $68.21   $68.20   $68.20  
  Purchase #2 $51.69   5.341%   $54.4508   $54.45   $54.45   $54.50  
  Purchase #3 $244.39   11.197%   $271.7543   $271.75   $271.75   $271.80  
  Purchase #4 $235.25   7.373%   $252.595   $252.60   $252.60   $252.60  
  Purchase #5 $153.57   9.286%   $167.8305   $167.83   $167.85   $167.80  
  Purchase #6 $21.78   5.604%   $23.0006   $23.00   $23.00   $23.00  
  Purchase #7 $42.94   3.340%   $44.3742   $44.37   $44.35   $44.40  
  7 purchase totals = $811.31       $882.2185   $882.21   $882.20   $882.30