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 $239.48   11.495%   $267.0082   $267.01   $267.00   $267.00  
  Purchase #2 $8.87   10.133%   $9.7688   $9.77   $9.75   $9.80  
  Purchase #3 $62.50   7.480%   $67.175   $67.18   $67.20   $67.20  
  Purchase #4 $189.76   3.358%   $196.1321   $196.13   $196.15   $196.10  
  Purchase #5 $152.25   8.282%   $164.8593   $164.86   $164.85   $164.90  
  Purchase #6 $249.84   13.388%   $283.2886   $283.29   $283.30   $283.30  
  Purchase #7 $224.40   13.497%   $254.6873   $254.69   $254.70   $254.70  
  7 purchase totals = $1,127.10       $1,242.9193   $1,242.93   $1,242.95   $1,243.00