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 $61.83   12.788%   $69.7368   $69.74   $69.75   $69.70  
  Purchase #2 $139.40   4.487%   $145.6549   $145.65   $145.65   $145.70  
  Purchase #3 $112.41   3.321%   $116.1431   $116.14   $116.15   $116.10  
  Purchase #4 $123.94   7.528%   $133.2702   $133.27   $133.25   $133.30  
  Purchase #5 $152.63   12.532%   $171.7576   $171.76   $171.75   $171.80  
  Purchase #6 $129.49   3.871%   $134.5026   $134.50   $134.50   $134.50  
  Purchase #7 $29.94   6.669%   $31.9367   $31.94   $31.95   $31.90  
  7 purchase totals = $749.64       $803.0019   $803.00   $803.00   $803.00