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	$47.57	5.176%	$50.0322	$50.03	$50.05	$50.00
Purchase #2	$195.43	9.655%	$214.2988	$214.30	$214.30	$214.30
Purchase #3	$33.76	13.420%	$38.2906	$38.29	$38.30	$38.30
Purchase #4	$68.72	12.720%	$77.4612	$77.46	$77.45	$77.50
Purchase #5	$99.65	6.839%	$106.4651	$106.47	$106.45	$106.50
Purchase #6	$56.39	5.419%	$59.4458	$59.45	$59.45	$59.40
Purchase #7	$215.52	3.490%	$223.0416	$223.04	$223.05	$223.00
7 purchase totals =	$717.04		$769.0353	$769.04	$769.05	$769.00