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 $78.50   7.342%   $84.2635   $84.26   $84.25   $84.30  
  Purchase #2 $53.73   4.466%   $56.1296   $56.13   $56.15   $56.10  
  Purchase #3 $182.29   8.328%   $197.4711   $197.47   $197.45   $197.50  
  Purchase #4 $86.86   8.164%   $93.9513   $93.95   $93.95   $94.00  
  Purchase #5 $148.92   9.339%   $162.8276   $162.83   $162.85   $162.80  
  Purchase #6 $177.87   13.321%   $201.5641   $201.56   $201.55   $201.60  
  Purchase #7 $164.84   5.331%   $173.6276   $173.63   $173.65   $173.60  
  7 purchase totals = $893.01       $969.8348   $969.83   $969.85   $969.90