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 $183.47   6.185%   $194.8176   $194.82   $194.80   $194.80  
  Purchase #2 $118.67   10.746%   $131.4223   $131.42   $131.40   $131.40  
  Purchase #3 $164.34   7.420%   $176.534   $176.53   $176.55   $176.50  
  Purchase #4 $118.27   8.141%   $127.8984   $127.90   $127.90   $127.90  
  Purchase #5 $217.46   3.219%   $224.46   $224.46   $224.45   $224.50  
  Purchase #6 $235.55   6.820%   $251.6145   $251.61   $251.60   $251.60  
  Purchase #7 $86.53   11.750%   $96.6973   $96.70   $96.70   $96.70  
  7 purchase totals = $1,124.29       $1,203.4441   $1,203.44   $1,203.40   $1,203.40