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 $246.92   6.216%   $262.2685   $262.27   $262.25   $262.30  
  Purchase #2 $143.78   11.133%   $159.787   $159.79   $159.80   $159.80  
  Purchase #3 $133.37   6.577%   $142.1417   $142.14   $142.15   $142.10  
  Purchase #4 $250.57   10.347%   $276.4965   $276.50   $276.50   $276.50  
  Purchase #5 $67.93   9.267%   $74.2251   $74.23   $74.25   $74.20  
  Purchase #6 $50.38   4.599%   $52.697   $52.70   $52.70   $52.70  
  Purchase #7 $227.67   8.619%   $247.2929   $247.29   $247.30   $247.30  
  7 purchase totals = $1,120.62       $1,214.9087   $1,214.92   $1,214.95   $1,214.90