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 $246.28   11.160%   $273.7648   $273.76   $273.75   $273.80  
  Purchase #2 $226.52   13.381%   $256.8306   $256.83   $256.85   $256.80  
  Purchase #3 $232.48   6.208%   $246.9124   $246.91   $246.90   $246.90  
  Purchase #4 $13.36   11.306%   $14.8705   $14.87   $14.85   $14.90  
  Purchase #5 $124.61   9.108%   $135.9595   $135.96   $135.95   $136.00  
  Purchase #6 $242.26   3.399%   $250.4944   $250.49   $250.50   $250.50  
  Purchase #7 $44.41   8.152%   $48.0303   $48.03   $48.05   $48.00  
  7 purchase totals = $1,129.92       $1,226.8625   $1,226.85   $1,226.85   $1,226.90