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 $173.73   6.820%   $185.5784   $185.58   $185.60   $185.60  
  Purchase #2 $51.94   4.636%   $54.3479   $54.35   $54.35   $54.30  
  Purchase #3 $152.47   5.587%   $160.9885   $160.99   $161.00   $161.00  
  Purchase #4 $174.44   6.857%   $186.4014   $186.40   $186.40   $186.40  
  Purchase #5 $186.37   4.687%   $195.1052   $195.11   $195.10   $195.10  
  Purchase #6 $125.62   9.709%   $137.8164   $137.82   $137.80   $137.80  
  Purchase #7 $69.55   6.794%   $74.2752   $74.28   $74.30   $74.30  
  7 purchase totals = $934.12       $994.5130   $994.53   $994.55   $994.50