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 $51.96   13.214%   $58.826   $58.83   $58.85   $58.80  
  Purchase #2 $205.61   6.265%   $218.4915   $218.49   $218.50   $218.50  
  Purchase #3 $133.94   8.141%   $144.8441   $144.84   $144.85   $144.80  
  Purchase #4 $114.62   7.280%   $122.9643   $122.96   $122.95   $123.00  
  Purchase #5 $85.44   6.800%   $91.2499   $91.25   $91.25   $91.20  
  Purchase #6 $101.98   4.281%   $106.3458   $106.35   $106.35   $106.30  
  Purchase #7 $72.87   11.835%   $81.4942   $81.49   $81.50   $81.50  
  7 purchase totals = $766.42       $824.2158   $824.21   $824.25   $824.10