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	$50.36	8.736%	$54.7594	$54.76	$54.75	$54.80
Purchase #2	$92.50	7.494%	$99.432	$99.43	$99.45	$99.40
Purchase #3	$47.80	3.699%	$49.5681	$49.57	$49.55	$49.60
Purchase #4	$116.56	6.271%	$123.8695	$123.87	$123.85	$123.90
Purchase #5	$52.56	5.634%	$55.5212	$55.52	$55.50	$55.50
Purchase #6	$173.49	8.253%	$187.8081	$187.81	$187.80	$187.80
Purchase #7	$204.41	8.298%	$221.3719	$221.37	$221.35	$221.40
7 purchase totals =	$737.68		$792.3302	$792.33	$792.25	$792.40