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 $236.84   11.211%   $263.3921   $263.39   $263.40   $263.40  
  Purchase #2 $112.33   8.728%   $122.1342   $122.13   $122.15   $122.10  
  Purchase #3 $117.76   6.307%   $125.1871   $125.19   $125.20   $125.20  
  Purchase #4 $208.41   5.273%   $219.3995   $219.40   $219.40   $219.40  
  Purchase #5 $41.85   7.624%   $45.0406   $45.04   $45.05   $45.00  
  Purchase #6 $39.32   6.783%   $41.9871   $41.99   $42.00   $42.00  
  Purchase #7 $231.31   5.569%   $244.1917   $244.19   $244.20   $244.20  
  7 purchase totals = $987.82       $1,061.3323   $1,061.33   $1,061.40   $1,061.30