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 $125.64   11.650%   $140.2771   $140.28   $140.30   $140.30  
  Purchase #2 $197.46   13.551%   $224.2178   $224.22   $224.20   $224.20  
  Purchase #3 $180.89   11.112%   $200.9905   $200.99   $201.00   $201.00  
  Purchase #4 $67.54   6.565%   $71.974   $71.97   $71.95   $72.00  
  Purchase #5 $148.34   7.120%   $158.9018   $158.90   $158.90   $158.90  
  Purchase #6 $206.76   8.660%   $224.6654   $224.67   $224.65   $224.70  
  Purchase #7 $87.76   12.331%   $98.5817   $98.58   $98.60   $98.60  
  7 purchase totals = $1,014.39       $1,119.6083   $1,119.61   $1,119.60   $1,119.70