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 $78.36   7.824%   $84.4909   $84.49   $84.50   $84.50  
  Purchase #2 $188.40   5.758%   $199.2481   $199.25   $199.25   $199.20  
  Purchase #3 $243.77   5.374%   $256.8702   $256.87   $256.85   $256.90  
  Purchase #4 $162.82   8.819%   $177.1791   $177.18   $177.20   $177.20  
  Purchase #5 $111.42   4.653%   $116.6044   $116.60   $116.60   $116.60  
  Purchase #6 $105.25   11.413%   $117.2622   $117.26   $117.25   $117.30  
  Purchase #7 $69.53   7.520%   $74.7587   $74.76   $74.75   $74.80  
  7 purchase totals = $959.55       $1,026.4136   $1,026.41   $1,026.40   $1,026.50