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 $53.97   12.520%   $60.727   $60.73   $60.75   $60.70  
  Purchase #2 $234.84   7.749%   $253.0378   $253.04   $253.05   $253.00  
  Purchase #3 $172.42   11.466%   $192.1897   $192.19   $192.20   $192.20  
  Purchase #4 $116.95   11.758%   $130.701   $130.70   $130.70   $130.70  
  Purchase #5 $130.86   9.454%   $143.2315   $143.23   $143.25   $143.20  
  Purchase #6 $63.89   5.262%   $67.2519   $67.25   $67.25   $67.30  
  Purchase #7 $5.37   8.149%   $5.8076   $5.81   $5.80   $5.80  
  7 purchase totals = $778.30       $852.9465   $852.95   $853.00   $852.90