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	$80.85	10.463%	$89.3093	$89.31	$89.30	$89.30
Purchase #2	$33.41	5.120%	$35.1206	$35.12	$35.10	$35.10
Purchase #3	$102.67	10.634%	$113.5879	$113.59	$113.60	$113.60
Purchase #4	$80.57	9.117%	$87.9156	$87.92	$87.90	$87.90
Purchase #5	$187.63	12.811%	$211.6673	$211.67	$211.65	$211.70
Purchase #6	$63.83	13.709%	$72.5805	$72.58	$72.60	$72.60
Purchase #7	$118.46	9.783%	$130.0489	$130.05	$130.05	$130.00
7 purchase totals =	$667.42		$740.2301	$740.24	$740.20	$740.20