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	$39.65	13.604%	$45.044	$45.04	$45.05	$45.00
Purchase #2	$83.72	10.775%	$92.7408	$92.74	$92.75	$92.70
Purchase #3	$181.47	6.711%	$193.6485	$193.65	$193.65	$193.60
Purchase #4	$85.44	11.585%	$95.3382	$95.34	$95.35	$95.30
Purchase #5	$98.83	12.707%	$111.3883	$111.39	$111.40	$111.40
Purchase #6	$86.47	3.420%	$89.4273	$89.43	$89.45	$89.40
Purchase #7	$175.56	4.468%	$183.404	$183.40	$183.40	$183.40
7 purchase totals =	$751.14		$810.9911	$810.99	$811.05	$810.80