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	$44.71	13.323%	$50.6667	$50.67	$50.65	$50.70
Purchase #2	$188.68	13.271%	$213.7197	$213.72	$213.70	$213.70
Purchase #3	$157.38	9.656%	$172.5766	$172.58	$172.60	$172.60
Purchase #4	$89.50	6.255%	$95.0982	$95.10	$95.10	$95.10
Purchase #5	$36.38	10.623%	$40.2446	$40.24	$40.25	$40.20
Purchase #6	$31.82	9.622%	$34.8817	$34.88	$34.90	$34.90
Purchase #7	$179.61	3.311%	$185.5569	$185.56	$185.55	$185.60
7 purchase totals =	$728.08		$792.7444	$792.75	$792.75	$792.80