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	$85.60	6.641%	$91.2847	$91.28	$91.30	$91.30
Purchase #2	$74.76	5.567%	$78.9219	$78.92	$78.90	$78.90
Purchase #3	$28.59	8.666%	$31.0676	$31.07	$31.05	$31.10
Purchase #4	$127.67	9.249%	$139.4782	$139.48	$139.50	$139.50
Purchase #5	$139.41	11.497%	$155.438	$155.44	$155.45	$155.40
Purchase #6	$217.56	5.239%	$228.958	$228.96	$228.95	$229.00
Purchase #7	$40.38	12.194%	$45.3039	$45.30	$45.30	$45.30
7 purchase totals =	$713.97		$770.4523	$770.45	$770.45	$770.50