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	$86.40	3.492%	$89.4171	$89.42	$89.40	$89.40
Purchase #2	$89.54	11.734%	$100.0466	$100.05	$100.05	$100.00
Purchase #3	$178.46	7.640%	$192.0943	$192.09	$192.10	$192.10
Purchase #4	$250.65	9.826%	$275.2789	$275.28	$275.30	$275.30
Purchase #5	$180.82	6.583%	$192.7234	$192.72	$192.70	$192.70
Purchase #6	$65.38	9.494%	$71.5872	$71.59	$71.60	$71.60
Purchase #7	$179.95	12.757%	$202.9062	$202.91	$202.90	$202.90
7 purchase totals =	$1,031.20		$1,124.0537	$1,124.06	$1,124.05	$1,124.00