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	$33.77	9.641%	$37.0258	$37.03	$37.05	$37.00
Purchase #2	$67.25	10.248%	$74.1418	$74.14	$74.15	$74.10
Purchase #3	$62.49	4.298%	$65.1758	$65.18	$65.20	$65.20
Purchase #4	$115.78	13.492%	$131.401	$131.40	$131.40	$131.40
Purchase #5	$68.33	4.634%	$71.4964	$71.50	$71.50	$71.50
Purchase #6	$49.93	9.312%	$54.5795	$54.58	$54.60	$54.60
Purchase #7	$202.32	4.537%	$211.4993	$211.50	$211.50	$211.50
7 purchase totals =	$599.87		$645.3196	$645.33	$645.40	$645.30