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	$79.74	4.186%	$83.0779	$83.08	$83.10	$83.10
Purchase #2	$85.84	5.416%	$90.4891	$90.49	$90.50	$90.50
Purchase #3	$99.71	9.304%	$108.987	$108.99	$109.00	$109.00
Purchase #4	$113.74	13.475%	$129.0665	$129.07	$129.05	$129.10
Purchase #5	$72.95	7.277%	$78.2586	$78.26	$78.25	$78.30
Purchase #6	$159.45	8.430%	$172.8916	$172.89	$172.90	$172.90
Purchase #7	$196.33	5.322%	$206.7787	$206.78	$206.80	$206.80
7 purchase totals =	$807.76		$869.5494	$869.56	$869.60	$869.70