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	$85.88	4.341%	$89.6081	$89.61	$89.60	$89.60
Purchase #2	$113.80	11.731%	$127.1499	$127.15	$127.15	$127.10
Purchase #3	$69.61	11.613%	$77.6938	$77.69	$77.70	$77.70
Purchase #4	$216.25	10.550%	$239.0644	$239.06	$239.05	$239.10
Purchase #5	$46.28	11.712%	$51.7003	$51.70	$51.70	$51.70
Purchase #6	$146.74	10.558%	$162.2328	$162.23	$162.25	$162.20
Purchase #7	$150.57	12.311%	$169.1067	$169.11	$169.10	$169.10
7 purchase totals =	$829.13		$916.5560	$916.55	$916.55	$916.50