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 $239.53   9.725%   $262.8243   $262.82   $262.80   $262.80  
  Purchase #2 $43.63   6.121%   $46.3006   $46.30   $46.30   $46.30  
  Purchase #3 $224.52   11.873%   $251.1773   $251.18   $251.20   $251.20  
  Purchase #4 $238.27   5.867%   $252.2493   $252.25   $252.25   $252.20  
  Purchase #5 $228.26   11.595%   $254.7267   $254.73   $254.75   $254.70  
  Purchase #6 $134.81   12.627%   $151.8325   $151.83   $151.85   $151.80  
  Purchase #7 $194.97   7.549%   $209.6883   $209.69   $209.70   $209.70  
  7 purchase totals = $1,303.99       $1,428.7990   $1,428.80   $1,428.85   $1,428.70