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	$218.59	6.834%	$233.5284	$233.53	$233.55	$233.50
Purchase #2	$132.76	13.457%	$150.6255	$150.63	$150.65	$150.60
Purchase #3	$133.96	11.539%	$149.4176	$149.42	$149.40	$149.40
Purchase #4	$125.78	4.841%	$131.869	$131.87	$131.85	$131.90
Purchase #5	$133.31	4.492%	$139.2983	$139.30	$139.30	$139.30
Purchase #6	$34.67	7.659%	$37.3254	$37.33	$37.35	$37.30
Purchase #7	$239.49	6.289%	$254.5515	$254.55	$254.55	$254.60
7 purchase totals =	$1,018.56		$1,096.6157	$1,096.63	$1,096.65	$1,096.60