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	$13.72	9.472%	$15.0196	$15.02	$15.00	$15.00
Purchase #2	$249.49	4.309%	$260.2405	$260.24	$260.25	$260.20
Purchase #3	$105.55	6.551%	$112.4646	$112.46	$112.45	$112.50
Purchase #4	$135.71	9.687%	$148.8562	$148.86	$148.85	$148.90
Purchase #5	$98.33	7.291%	$105.4992	$105.50	$105.50	$105.50
Purchase #6	$31.54	13.753%	$35.8777	$35.88	$35.90	$35.90
Purchase #7	$184.68	6.471%	$196.6306	$196.63	$196.65	$196.60
7 purchase totals =	$819.02		$874.5884	$874.59	$874.60	$874.60