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 $33.84   6.195%   $35.9364   $35.94   $35.95   $35.90  
  Purchase #2 $224.91   11.752%   $251.3414   $251.34   $251.35   $251.30  
  Purchase #3 $231.53   11.690%   $258.5959   $258.60   $258.60   $258.60  
  Purchase #4 $17.34   11.682%   $19.3657   $19.37   $19.35   $19.40  
  Purchase #5 $11.97   7.115%   $12.8217   $12.82   $12.80   $12.80  
  Purchase #6 $157.49   5.210%   $165.6952   $165.70   $165.70   $165.70  
  Purchase #7 $111.44   12.378%   $125.234   $125.23   $125.25   $125.20  
  7 purchase totals = $788.52       $868.9903   $869.00   $869.00   $868.90