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 $156.45   12.687%   $176.2988   $176.30   $176.30   $176.30  
  Purchase #2 $220.34   4.488%   $230.2289   $230.23   $230.25   $230.20  
  Purchase #3 $107.37   8.607%   $116.6113   $116.61   $116.60   $116.60  
  Purchase #4 $26.63   12.172%   $29.8714   $29.87   $29.85   $29.90  
  Purchase #5 $86.73   9.537%   $95.0014   $95.00   $95.00   $95.00  
  Purchase #6 $51.47   5.490%   $54.2957   $54.30   $54.30   $54.30  
  Purchase #7 $177.28   8.111%   $191.6592   $191.66   $191.65   $191.70  
  7 purchase totals = $826.27       $893.9667   $893.97   $893.95   $894.00