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 $76.79   11.681%   $85.7598   $85.76   $85.75   $85.80  
  Purchase #2 $188.70   7.758%   $203.3393   $203.34   $203.35   $203.30  
  Purchase #3 $243.55   8.561%   $264.4003   $264.40   $264.40   $264.40  
  Purchase #4 $70.80   3.562%   $73.3219   $73.32   $73.30   $73.30  
  Purchase #5 $158.31   4.241%   $165.0239   $165.02   $165.00   $165.00  
  Purchase #6 $248.76   7.703%   $267.922   $267.92   $267.90   $267.90  
  Purchase #7 $240.26   9.111%   $262.1501   $262.15   $262.15   $262.20  
  7 purchase totals = $1,227.17       $1,321.9173   $1,321.91   $1,321.85   $1,321.90