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	$50.96	5.192%	$53.6058	$53.61	$53.60	$53.60
Purchase #2	$34.51	5.655%	$36.4615	$36.46	$36.45	$36.50
Purchase #3	$141.70	12.491%	$159.3997	$159.40	$159.40	$159.40
Purchase #4	$55.27	8.285%	$59.8491	$59.85	$59.85	$59.80
Purchase #5	$133.29	4.696%	$139.5493	$139.55	$139.55	$139.50
Purchase #6	$129.74	12.663%	$146.169	$146.17	$146.15	$146.20
Purchase #7	$83.83	13.114%	$94.8235	$94.82	$94.80	$94.80
7 purchase totals =	$629.30		$689.8579	$689.86	$689.80	$689.80