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 $236.61   11.748%   $264.4069   $264.41   $264.40   $264.40  
  Purchase #2 $65.42   12.678%   $73.7139   $73.71   $73.70   $73.70  
  Purchase #3 $25.39   6.583%   $27.0614   $27.06   $27.05   $27.10  
  Purchase #4 $246.65   11.722%   $275.5623   $275.56   $275.55   $275.60  
  Purchase #5 $170.66   13.806%   $194.2213   $194.22   $194.20   $194.20  
  Purchase #6 $248.64   11.807%   $277.9969   $278.00   $278.00   $278.00  
  Purchase #7 $8.42   10.855%   $9.334   $9.33   $9.35   $9.30  
  7 purchase totals = $1,001.79       $1,122.2967   $1,122.29   $1,122.25   $1,122.30