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	$177.97	6.642%	$189.7908	$189.79	$189.80	$189.80
Purchase #2	$236.58	13.448%	$268.3953	$268.40	$268.40	$268.40
Purchase #3	$48.64	7.851%	$52.4587	$52.46	$52.45	$52.50
Purchase #4	$91.46	4.844%	$95.8903	$95.89	$95.90	$95.90
Purchase #5	$6.43	13.641%	$7.3071	$7.31	$7.30	$7.30
Purchase #6	$196.66	12.641%	$221.5198	$221.52	$221.50	$221.50
Purchase #7	$10.37	3.365%	$10.719	$10.72	$10.70	$10.70
7 purchase totals =	$768.11		$846.0810	$846.09	$846.05	$846.10