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 $185.81   7.664%   $200.0505   $200.05   $200.05   $200.10  
  Purchase #2 $63.43   4.319%   $66.1695   $66.17   $66.15   $66.20  
  Purchase #3 $47.57   3.745%   $49.3515   $49.35   $49.35   $49.40  
  Purchase #4 $129.67   4.769%   $135.854   $135.85   $135.85   $135.90  
  Purchase #5 $120.56   4.544%   $126.0382   $126.04   $126.05   $126.00  
  Purchase #6 $188.40   5.828%   $199.38   $199.38   $199.40   $199.40  
  Purchase #7 $44.71   4.435%   $46.6929   $46.69   $46.70   $46.70  
  7 purchase totals = $780.15       $823.5366   $823.53   $823.55   $823.70