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	$13.98	9.833%	$15.3547	$15.35	$15.35	$15.40
Purchase #2	$75.90	13.453%	$86.1108	$86.11	$86.10	$86.10
Purchase #3	$222.39	7.419%	$238.8891	$238.89	$238.90	$238.90
Purchase #4	$81.59	5.189%	$85.8237	$85.82	$85.80	$85.80
Purchase #5	$213.67	12.673%	$240.7484	$240.75	$240.75	$240.70
Purchase #6	$43.70	7.360%	$46.9163	$46.92	$46.90	$46.90
Purchase #7	$74.59	4.605%	$78.0249	$78.02	$78.00	$78.00
7 purchase totals =	$725.82		$791.8679	$791.86	$791.80	$791.80