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	$113.54	12.548%	$127.787	$127.79	$127.80	$127.80
Purchase #2	$170.26	12.544%	$191.6174	$191.62	$191.60	$191.60
Purchase #3	$69.68	5.830%	$73.7423	$73.74	$73.75	$73.70
Purchase #4	$144.49	9.683%	$158.481	$158.48	$158.50	$158.50
Purchase #5	$114.73	8.453%	$124.4281	$124.43	$124.45	$124.40
Purchase #6	$149.31	12.560%	$168.0633	$168.06	$168.05	$168.10
Purchase #7	$71.53	9.798%	$78.5385	$78.54	$78.55	$78.50
7 purchase totals =	$833.54		$922.6576	$922.66	$922.70	$922.60