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	$85.87	3.518%	$88.8909	$88.89	$88.90	$88.90
Purchase #2	$136.82	9.271%	$149.5046	$149.50	$149.50	$149.50
Purchase #3	$37.25	4.167%	$38.8022	$38.80	$38.80	$38.80
Purchase #4	$108.84	6.744%	$116.1802	$116.18	$116.20	$116.20
Purchase #5	$78.61	13.803%	$89.4605	$89.46	$89.45	$89.50
Purchase #6	$149.84	10.712%	$165.8909	$165.89	$165.90	$165.90
Purchase #7	$35.75	10.656%	$39.5595	$39.56	$39.55	$39.60
7 purchase totals =	$632.98		$688.2888	$688.28	$688.30	$688.40