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	$242.32	3.300%	$250.3166	$250.32	$250.30	$250.30
Purchase #2	$48.77	12.465%	$54.8492	$54.85	$54.85	$54.80
Purchase #3	$58.96	11.486%	$65.7321	$65.73	$65.75	$65.70
Purchase #4	$242.55	5.564%	$256.0455	$256.05	$256.05	$256.00
Purchase #5	$107.33	3.798%	$111.4064	$111.41	$111.40	$111.40
Purchase #6	$181.54	11.621%	$202.6368	$202.64	$202.65	$202.60
Purchase #7	$140.26	6.190%	$148.9421	$148.94	$148.95	$148.90
7 purchase totals =	$1,021.73		$1,089.9287	$1,089.94	$1,089.95	$1,089.70