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 $214.69   4.432%   $224.2051   $224.21   $224.20   $224.20  
  Purchase #2 $56.97   3.381%   $58.8962   $58.90   $58.90   $58.90  
  Purchase #3 $221.90   13.194%   $251.1775   $251.18   $251.20   $251.20  
  Purchase #4 $141.46   6.874%   $151.184   $151.18   $151.20   $151.20  
  Purchase #5 $155.27   12.718%   $175.0172   $175.02   $175.00   $175.00  
  Purchase #6 $68.68   11.573%   $76.6283   $76.63   $76.65   $76.60  
  Purchase #7 $6.87   6.362%   $7.3071   $7.31   $7.30   $7.30  
  7 purchase totals = $865.84       $944.4154   $944.43   $944.45   $944.40