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 $58.44   8.655%   $63.498   $63.50   $63.50   $63.50  
  Purchase #2 $227.64   6.390%   $242.1862   $242.19   $242.20   $242.20  
  Purchase #3 $26.48   5.150%   $27.8437   $27.84   $27.85   $27.80  
  Purchase #4 $42.68   13.519%   $48.4499   $48.45   $48.45   $48.40  
  Purchase #5 $32.85   11.205%   $36.5308   $36.53   $36.55   $36.50  
  Purchase #6 $156.54   6.326%   $166.4427   $166.44   $166.45   $166.40  
  Purchase #7 $12.64   12.598%   $14.2324   $14.23   $14.25   $14.20  
  7 purchase totals = $557.27       $599.1837   $599.18   $599.25   $599.00