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	$97.50	4.861%	$102.2395	$102.24	$102.25	$102.20
Purchase #2	$171.26	5.821%	$181.229	$181.23	$181.25	$181.20
Purchase #3	$81.61	9.667%	$89.4992	$89.50	$89.50	$89.50
Purchase #4	$184.91	13.475%	$209.8266	$209.83	$209.85	$209.80
Purchase #5	$18.66	6.133%	$19.8044	$19.80	$19.80	$19.80
Purchase #6	$92.69	13.564%	$105.2625	$105.26	$105.25	$105.30
Purchase #7	$91.51	9.485%	$100.1897	$100.19	$100.20	$100.20
7 purchase totals =	$738.14		$808.0509	$808.05	$808.10	$808.00