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 $161.85   3.226%   $167.0713   $167.07   $167.05   $167.10  
  Purchase #2 $227.94   5.735%   $241.0124   $241.01   $241.00   $241.00  
  Purchase #3 $205.95   6.592%   $219.5262   $219.53   $219.55   $219.50  
  Purchase #4 $242.40   7.839%   $261.4017   $261.40   $261.40   $261.40  
  Purchase #5 $37.93   10.526%   $41.9225   $41.92   $41.90   $41.90  
  Purchase #6 $191.97   10.568%   $212.2574   $212.26   $212.25   $212.30  
  Purchase #7 $162.79   12.561%   $183.2381   $183.24   $183.25   $183.20  
  7 purchase totals = $1,230.83       $1,326.4296   $1,326.43   $1,326.40   $1,326.40