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	$127.87	12.821%	$144.2642	$144.26	$144.25	$144.30
Purchase #2	$72.54	7.596%	$78.0501	$78.05	$78.05	$78.10
Purchase #3	$104.58	8.576%	$113.5488	$113.55	$113.55	$113.50
Purchase #4	$223.46	13.541%	$253.7187	$253.72	$253.70	$253.70
Purchase #5	$60.71	11.553%	$67.7238	$67.72	$67.70	$67.70
Purchase #6	$241.47	9.839%	$265.2282	$265.23	$265.25	$265.20
Purchase #7	$239.56	6.200%	$254.4127	$254.41	$254.40	$254.40
7 purchase totals =	$1,070.19		$1,176.9465	$1,176.94	$1,176.90	$1,176.90