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 $243.77   7.702%   $262.5452   $262.55   $262.55   $262.50  
  Purchase #2 $188.49   8.856%   $205.1827   $205.18   $205.20   $205.20  
  Purchase #3 $149.26   9.859%   $163.9755   $163.98   $164.00   $164.00  
  Purchase #4 $91.46   6.657%   $97.5485   $97.55   $97.55   $97.50  
  Purchase #5 $245.69   11.377%   $273.6422   $273.64   $273.65   $273.60  
  Purchase #6 $250.93   9.137%   $273.8575   $273.86   $273.85   $273.90  
  Purchase #7 $55.25   11.822%   $61.7817   $61.78   $61.80   $61.80  
  7 purchase totals = $1,224.85       $1,338.5333   $1,338.54   $1,338.60   $1,338.50