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	$160.99	7.656%	$173.3154	$173.32	$173.30	$173.30
Purchase #2	$152.26	7.429%	$163.5714	$163.57	$163.55	$163.60
Purchase #3	$131.74	10.106%	$145.0536	$145.05	$145.05	$145.10
Purchase #4	$77.40	11.176%	$86.0502	$86.05	$86.05	$86.10
Purchase #5	$37.56	9.597%	$41.1646	$41.16	$41.15	$41.20
Purchase #6	$85.41	4.373%	$89.145	$89.15	$89.15	$89.10
Purchase #7	$182.88	7.442%	$196.4899	$196.49	$196.50	$196.50
7 purchase totals =	$828.24		$894.7901	$894.79	$894.75	$894.90