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 $246.32   11.665%   $275.0532   $275.05   $275.05   $275.10  
  Purchase #2 $74.31   11.496%   $82.8527   $82.85   $82.85   $82.90  
  Purchase #3 $97.79   7.830%   $105.447   $105.45   $105.45   $105.40  
  Purchase #4 $157.55   13.365%   $178.6066   $178.61   $178.60   $178.60  
  Purchase #5 $237.95   4.773%   $249.3074   $249.31   $249.30   $249.30  
  Purchase #6 $192.62   5.514%   $203.2411   $203.24   $203.25   $203.20  
  Purchase #7 $23.27   5.868%   $24.6355   $24.64   $24.65   $24.60  
  7 purchase totals = $1,029.81       $1,119.1435   $1,119.15   $1,119.15   $1,119.10