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 $24.26   6.353%   $25.8012   $25.80   $25.80   $25.80  
  Purchase #2 $137.47   9.447%   $150.4568   $150.46   $150.45   $150.50  
  Purchase #3 $24.78   7.388%   $26.6107   $26.61   $26.60   $26.60  
  Purchase #4 $90.91   7.536%   $97.761   $97.76   $97.75   $97.80  
  Purchase #5 $208.85   11.582%   $233.039   $233.04   $233.05   $233.00  
  Purchase #6 $229.94   6.276%   $244.371   $244.37   $244.35   $244.40  
  Purchase #7 $80.90   12.514%   $91.0238   $91.02   $91.00   $91.00  
  7 purchase totals = $797.11       $869.0635   $869.06   $869.00   $869.10