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 $246.59   8.788%   $268.2603   $268.26   $268.25   $268.30  
  Purchase #2 $176.90   12.340%   $198.7295   $198.73   $198.75   $198.70  
  Purchase #3 $105.87   6.332%   $112.5737   $112.57   $112.55   $112.60  
  Purchase #4 $180.61   8.429%   $195.8336   $195.83   $195.85   $195.80  
  Purchase #5 $187.35   12.722%   $211.1847   $211.18   $211.20   $211.20  
  Purchase #6 $19.28   4.425%   $20.1331   $20.13   $20.15   $20.10  
  Purchase #7 $8.64   5.289%   $9.097   $9.10   $9.10   $9.10  
  7 purchase totals = $925.24       $1,015.8119   $1,015.80   $1,015.85   $1,015.80