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	$99.79	4.280%	$104.061	$104.06	$104.05	$104.10
Purchase #2	$153.56	11.147%	$170.6773	$170.68	$170.70	$170.70
Purchase #3	$162.61	5.848%	$172.1194	$172.12	$172.10	$172.10
Purchase #4	$90.97	10.319%	$100.3572	$100.36	$100.35	$100.40
Purchase #5	$115.28	7.552%	$123.9859	$123.99	$124.00	$124.00
Purchase #6	$53.43	4.714%	$55.9487	$55.95	$55.95	$55.90
Purchase #7	$158.69	11.434%	$176.8346	$176.83	$176.85	$176.80
7 purchase totals =	$834.33		$903.9841	$903.99	$904.00	$904.00