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	$145.46	4.297%	$151.7104	$151.71	$151.70	$151.70
Purchase #2	$249.87	7.187%	$267.8282	$267.83	$267.85	$267.80
Purchase #3	$98.82	13.684%	$112.3425	$112.34	$112.35	$112.30
Purchase #4	$72.77	7.294%	$78.0778	$78.08	$78.10	$78.10
Purchase #5	$72.91	6.538%	$77.6769	$77.68	$77.70	$77.70
Purchase #6	$247.27	10.619%	$273.5276	$273.53	$273.55	$273.50
Purchase #7	$20.54	7.435%	$22.0671	$22.07	$22.05	$22.10
7 purchase totals =	$907.64		$983.2305	$983.24	$983.30	$983.20