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	$72.84	9.717%	$79.9179	$79.92	$79.90	$79.90
Purchase #2	$76.85	11.352%	$85.574	$85.57	$85.55	$85.60
Purchase #3	$34.97	7.568%	$37.6165	$37.62	$37.60	$37.60
Purchase #4	$244.44	7.350%	$262.4063	$262.41	$262.40	$262.40
Purchase #5	$52.47	4.258%	$54.7042	$54.70	$54.70	$54.70
Purchase #6	$167.60	4.280%	$174.7733	$174.77	$174.75	$174.80
Purchase #7	$136.48	11.210%	$151.7794	$151.78	$151.80	$151.80
7 purchase totals =	$785.65		$846.7716	$846.77	$846.70	$846.80