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 $60.87   8.791%   $66.2211   $66.22   $66.20   $66.20  
  Purchase #2 $194.77   12.690%   $219.4863   $219.49   $219.50   $219.50  
  Purchase #3 $76.78   11.239%   $85.4093   $85.41   $85.40   $85.40  
  Purchase #4 $12.83   12.518%   $14.4361   $14.44   $14.45   $14.40  
  Purchase #5 $194.53   13.733%   $221.2448   $221.24   $221.25   $221.20  
  Purchase #6 $103.40   3.504%   $107.0231   $107.02   $107.00   $107.00  
  Purchase #7 $49.81   13.567%   $56.5677   $56.57   $56.55   $56.60  
  7 purchase totals = $692.99       $770.3884   $770.39   $770.35   $770.30