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 $32.27   11.585%   $36.0085   $36.01   $36.00   $36.00  
  Purchase #2 $36.85   4.577%   $38.5366   $38.54   $38.55   $38.50  
  Purchase #3 $60.90   8.226%   $65.9096   $65.91   $65.90   $65.90  
  Purchase #4 $130.53   4.466%   $136.3595   $136.36   $136.35   $136.40  
  Purchase #5 $13.73   10.119%   $15.1193   $15.12   $15.10   $15.10  
  Purchase #6 $209.34   4.255%   $218.2474   $218.25   $218.25   $218.20  
  Purchase #7 $223.30   10.507%   $246.7621   $246.76   $246.75   $246.80  
  7 purchase totals = $706.92       $756.9430   $756.95   $756.90   $756.90