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 $239.89   9.569%   $262.8451   $262.85   $262.85   $262.80  
  Purchase #2 $184.26   6.822%   $196.8302   $196.83   $196.85   $196.80  
  Purchase #3 $133.50   9.603%   $146.32   $146.32   $146.30   $146.30  
  Purchase #4 $154.89   13.775%   $176.2261   $176.23   $176.25   $176.20  
  Purchase #5 $222.83   13.682%   $253.3176   $253.32   $253.30   $253.30  
  Purchase #6 $8.30   4.674%   $8.6879   $8.69   $8.70   $8.70  
  Purchase #7 $17.44   12.366%   $19.5966   $19.60   $19.60   $19.60  
  7 purchase totals = $961.11       $1,063.8235   $1,063.84   $1,063.85   $1,063.70