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 $167.88   11.576%   $187.3138   $187.31   $187.30   $187.30  
  Purchase #2 $247.45   12.443%   $278.2402   $278.24   $278.25   $278.20  
  Purchase #3 $166.79   11.267%   $185.5822   $185.58   $185.60   $185.60  
  Purchase #4 $141.42   5.288%   $148.8983   $148.90   $148.90   $148.90  
  Purchase #5 $97.46   9.174%   $106.401   $106.40   $106.40   $106.40  
  Purchase #6 $164.38   6.443%   $174.971   $174.97   $174.95   $175.00  
  Purchase #7 $221.35   13.854%   $252.0158   $252.02   $252.00   $252.00  
  7 purchase totals = $1,206.73       $1,333.4223   $1,333.42   $1,333.40   $1,333.40