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 $17.31   13.185%   $19.5923   $19.59   $19.60   $19.60  
  Purchase #2 $245.42   3.191%   $253.2514   $253.25   $253.25   $253.30  
  Purchase #3 $200.49   3.222%   $206.9498   $206.95   $206.95   $206.90  
  Purchase #4 $233.82   4.523%   $244.3957   $244.40   $244.40   $244.40  
  Purchase #5 $60.27   3.206%   $62.2023   $62.20   $62.20   $62.20  
  Purchase #6 $241.72   3.694%   $250.6491   $250.65   $250.65   $250.60  
  Purchase #7 $25.44   4.269%   $26.526   $26.53   $26.55   $26.50  
  7 purchase totals = $1,024.47       $1,063.5666   $1,063.57   $1,063.60   $1,063.50