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	$82.51	8.702%	$89.69	$89.69	$89.70	$89.70
Purchase #2	$133.52	6.313%	$141.9491	$141.95	$141.95	$141.90
Purchase #3	$129.66	9.330%	$141.7573	$141.76	$141.75	$141.80
Purchase #4	$157.81	3.495%	$163.3255	$163.33	$163.35	$163.30
Purchase #5	$101.61	9.647%	$111.4123	$111.41	$111.40	$111.40
Purchase #6	$115.44	4.625%	$120.7791	$120.78	$120.80	$120.80
Purchase #7	$64.45	12.158%	$72.2858	$72.29	$72.30	$72.30
7 purchase totals =	$785.00		$841.1991	$841.21	$841.25	$841.20