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	$109.95	4.514%	$114.9131	$114.91	$114.90	$114.90
Purchase #2	$39.87	13.634%	$45.3059	$45.31	$45.30	$45.30
Purchase #3	$59.75	6.308%	$63.519	$63.52	$63.50	$63.50
Purchase #4	$228.30	11.356%	$254.2257	$254.23	$254.25	$254.20
Purchase #5	$45.84	11.297%	$51.0185	$51.02	$51.00	$51.00
Purchase #6	$183.55	10.123%	$202.1308	$202.13	$202.15	$202.10
Purchase #7	$85.74	4.758%	$89.8195	$89.82	$89.80	$89.80
7 purchase totals =	$753.00		$820.9325	$820.94	$820.90	$820.80