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	$104.26	6.556%	$111.0953	$111.10	$111.10	$111.10
Purchase #2	$158.28	13.728%	$180.0087	$180.01	$180.00	$180.00
Purchase #3	$165.29	9.187%	$180.4752	$180.48	$180.50	$180.50
Purchase #4	$80.40	11.775%	$89.8671	$89.87	$89.85	$89.90
Purchase #5	$10.50	12.427%	$11.8048	$11.80	$11.80	$11.80
Purchase #6	$120.95	7.847%	$130.4409	$130.44	$130.45	$130.40
Purchase #7	$172.84	6.868%	$184.7107	$184.71	$184.70	$184.70
7 purchase totals =	$812.52		$888.4027	$888.41	$888.40	$888.40