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	$102.94	8.218%	$111.3996	$111.40	$111.40	$111.40
Purchase #2	$94.38	11.562%	$105.2922	$105.29	$105.30	$105.30
Purchase #3	$221.62	10.334%	$244.5222	$244.52	$244.50	$244.50
Purchase #4	$190.70	6.134%	$202.3975	$202.40	$202.40	$202.40
Purchase #5	$92.49	5.337%	$97.4262	$97.43	$97.45	$97.40
Purchase #6	$43.46	4.565%	$45.4439	$45.44	$45.45	$45.40
Purchase #7	$44.74	13.466%	$50.7647	$50.76	$50.75	$50.80
7 purchase totals =	$790.33		$857.2463	$857.24	$857.25	$857.20