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 $94.91   13.402%   $107.6298   $107.63   $107.65   $107.60  
  Purchase #2 $241.82   4.128%   $251.8023   $251.80   $251.80   $251.80  
  Purchase #3 $175.50   7.537%   $188.7274   $188.73   $188.75   $188.70  
  Purchase #4 $201.91   6.430%   $214.8928   $214.89   $214.90   $214.90  
  Purchase #5 $203.68   5.668%   $215.2246   $215.22   $215.20   $215.20  
  Purchase #6 $124.35   6.524%   $132.4626   $132.46   $132.45   $132.50  
  Purchase #7 $66.42   8.357%   $71.9707   $71.97   $71.95   $72.00  
  7 purchase totals = $1,108.59       $1,182.7102   $1,182.70   $1,182.70   $1,182.70