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 $50.36   5.728%   $53.2446   $53.24   $53.25   $53.20  
  Purchase #2 $209.61   4.232%   $218.4807   $218.48   $218.50   $218.50  
  Purchase #3 $48.29   5.844%   $51.1121   $51.11   $51.10   $51.10  
  Purchase #4 $165.58   6.863%   $176.9438   $176.94   $176.95   $176.90  
  Purchase #5 $166.25   6.327%   $176.7686   $176.77   $176.75   $176.80  
  Purchase #6 $206.60   3.410%   $213.6451   $213.65   $213.65   $213.60  
  Purchase #7 $148.27   6.526%   $157.9461   $157.95   $157.95   $157.90  
  7 purchase totals = $994.96       $1,048.1410   $1,048.14   $1,048.15   $1,048.00