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 $23.73   12.796%   $26.7665   $26.77   $26.75   $26.80  
  Purchase #2 $93.67   4.362%   $97.7559   $97.76   $97.75   $97.80  
  Purchase #3 $76.29   8.368%   $82.6739   $82.67   $82.65   $82.70  
  Purchase #4 $157.84   11.451%   $175.9143   $175.91   $175.90   $175.90  
  Purchase #5 $199.80   5.702%   $211.1926   $211.19   $211.20   $211.20  
  Purchase #6 $130.29   4.385%   $136.0032   $136.00   $136.00   $136.00  
  Purchase #7 $236.93   11.488%   $264.1485   $264.15   $264.15   $264.10  
  7 purchase totals = $918.55       $994.4549   $994.45   $994.40   $994.50