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 $76.98   6.549%   $82.0214   $82.02   $82.00   $82.00  
  Purchase #2 $184.47   13.457%   $209.2941   $209.29   $209.30   $209.30  
  Purchase #3 $69.58   3.523%   $72.0313   $72.03   $72.05   $72.00  
  Purchase #4 $179.76   12.385%   $202.0233   $202.02   $202.00   $202.00  
  Purchase #5 $107.80   3.125%   $111.1688   $111.17   $111.15   $111.20  
  Purchase #6 $239.63   3.795%   $248.724   $248.72   $248.70   $248.70  
  Purchase #7 $202.86   6.275%   $215.5895   $215.59   $215.60   $215.60  
  7 purchase totals = $1,061.08       $1,140.8524   $1,140.84   $1,140.80   $1,140.80