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 $78.31   11.523%   $87.3337   $87.33   $87.35   $87.30  
  Purchase #2 $92.45   6.206%   $98.1874   $98.19   $98.20   $98.20  
  Purchase #3 $12.83   5.747%   $13.5673   $13.57   $13.55   $13.60  
  Purchase #4 $67.66   10.371%   $74.677   $74.68   $74.70   $74.70  
  Purchase #5 $33.57   7.330%   $36.0307   $36.03   $36.05   $36.00  
  Purchase #6 $249.29   6.331%   $265.0725   $265.07   $265.05   $265.10  
  Purchase #7 $183.26   4.397%   $191.3179   $191.32   $191.30   $191.30  
  7 purchase totals = $717.37       $766.1865   $766.19   $766.20   $766.20