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	$100.48	12.552%	$113.0922	$113.09	$113.10	$113.10
Purchase #2	$185.87	12.345%	$208.8157	$208.82	$208.80	$208.80
Purchase #3	$12.30	6.287%	$13.0733	$13.07	$13.05	$13.10
Purchase #4	$63.63	5.155%	$66.9101	$66.91	$66.90	$66.90
Purchase #5	$211.51	5.391%	$222.9125	$222.91	$222.90	$222.90
Purchase #6	$226.69	8.279%	$245.4577	$245.46	$245.45	$245.50
Purchase #7	$37.31	8.541%	$40.4966	$40.50	$40.50	$40.50
7 purchase totals =	$837.79		$910.7581	$910.76	$910.70	$910.80