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 $91.35   13.576%   $103.7517   $103.75   $103.75   $103.80  
  Purchase #2 $56.41   3.633%   $58.4594   $58.46   $58.45   $58.50  
  Purchase #3 $227.44   9.475%   $248.9899   $248.99   $249.00   $249.00  
  Purchase #4 $66.28   4.131%   $69.018   $69.02   $69.00   $69.00  
  Purchase #5 $148.74   12.670%   $167.5854   $167.59   $167.60   $167.60  
  Purchase #6 $224.29   5.160%   $235.8634   $235.86   $235.85   $235.90  
  Purchase #7 $158.84   13.660%   $180.5375   $180.54   $180.55   $180.50  
  7 purchase totals = $973.35       $1,064.2053   $1,064.21   $1,064.20   $1,064.30