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 $177.48   10.258%   $195.6859   $195.69   $195.70   $195.70  
  Purchase #2 $8.74   9.390%   $9.5607   $9.56   $9.55   $9.60  
  Purchase #3 $118.71   6.389%   $126.2944   $126.29   $126.30   $126.30  
  Purchase #4 $123.43   5.332%   $130.0113   $130.01   $130.00   $130.00  
  Purchase #5 $214.47   4.620%   $224.3785   $224.38   $224.40   $224.40  
  Purchase #6 $222.81   3.445%   $230.4858   $230.49   $230.50   $230.50  
  Purchase #7 $78.31   12.423%   $88.0385   $88.04   $88.05   $88.00  
  7 purchase totals = $943.95       $1,004.4551   $1,004.46   $1,004.50   $1,004.50