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 $236.27   4.373%   $246.6021   $246.60   $246.60   $246.60  
  Purchase #2 $95.99   8.720%   $104.3603   $104.36   $104.35   $104.40  
  Purchase #3 $86.49   5.201%   $90.9883   $90.99   $91.00   $91.00  
  Purchase #4 $92.99   8.614%   $101.0002   $101.00   $101.00   $101.00  
  Purchase #5 $70.29   4.406%   $73.387   $73.39   $73.40   $73.40  
  Purchase #6 $208.74   12.360%   $234.5403   $234.54   $234.55   $234.50  
  Purchase #7 $48.40   7.757%   $52.1544   $52.15   $52.15   $52.20  
  7 purchase totals = $839.17       $903.0326   $903.03   $903.05   $903.10