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	$226.54	6.344%	$240.9117	$240.91	$240.90	$240.90
Purchase #2	$179.86	9.199%	$196.4053	$196.41	$196.40	$196.40
Purchase #3	$114.45	12.265%	$128.4873	$128.49	$128.50	$128.50
Purchase #4	$60.68	8.370%	$65.7589	$65.76	$65.75	$65.80
Purchase #5	$160.78	6.821%	$171.7468	$171.75	$171.75	$171.70
Purchase #6	$242.30	5.305%	$255.154	$255.15	$255.15	$255.20
Purchase #7	$136.96	12.617%	$154.2402	$154.24	$154.25	$154.20
7 purchase totals =	$1,121.57		$1,212.7042	$1,212.71	$1,212.70	$1,212.70