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	$80.84	10.281%	$89.1512	$89.15	$89.15	$89.20
Purchase #2	$41.96	7.753%	$45.2132	$45.21	$45.20	$45.20
Purchase #3	$76.79	4.564%	$80.2947	$80.29	$80.30	$80.30
Purchase #4	$158.40	6.475%	$168.6564	$168.66	$168.65	$168.70
Purchase #5	$70.86	4.695%	$74.1869	$74.19	$74.20	$74.20
Purchase #6	$54.38	11.276%	$60.5119	$60.51	$60.50	$60.50
Purchase #7	$132.62	8.864%	$144.3754	$144.38	$144.40	$144.40
7 purchase totals =	$615.85		$662.3897	$662.39	$662.40	$662.50