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	$45.88	7.539%	$49.3389	$49.34	$49.35	$49.30
Purchase #2	$245.75	9.550%	$269.2191	$269.22	$269.20	$269.20
Purchase #3	$154.49	11.233%	$171.8439	$171.84	$171.85	$171.80
Purchase #4	$154.46	8.532%	$167.6385	$167.64	$167.65	$167.60
Purchase #5	$58.30	13.316%	$66.0632	$66.06	$66.05	$66.10
Purchase #6	$59.72	11.646%	$66.675	$66.68	$66.70	$66.70
Purchase #7	$54.86	8.174%	$59.3443	$59.34	$59.35	$59.30
7 purchase totals =	$773.46		$850.1229	$850.12	$850.15	$850.00