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 $244.41   4.230%   $254.7485   $254.75   $254.75   $254.70  
  Purchase #2 $15.70   9.823%   $17.2422   $17.24   $17.25   $17.20  
  Purchase #3 $104.49   13.212%   $118.2952   $118.30   $118.30   $118.30  
  Purchase #4 $123.56   11.557%   $137.8398   $137.84   $137.85   $137.80  
  Purchase #5 $42.69   13.688%   $48.5334   $48.53   $48.55   $48.50  
  Purchase #6 $201.62   9.283%   $220.3364   $220.34   $220.35   $220.30  
  Purchase #7 $200.90   12.469%   $225.9502   $225.95   $225.95   $226.00  
  7 purchase totals = $933.37       $1,022.9457   $1,022.95   $1,023.00   $1,022.80