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	$242.91	11.581%	$271.0414	$271.04	$271.05	$271.00
Purchase #2	$64.89	8.618%	$70.4822	$70.48	$70.50	$70.50
Purchase #3	$19.96	8.333%	$21.6233	$21.62	$21.60	$21.60
Purchase #4	$101.57	7.388%	$109.074	$109.07	$109.05	$109.10
Purchase #5	$99.56	12.198%	$111.7043	$111.70	$111.70	$111.70
Purchase #6	$109.35	9.812%	$120.0794	$120.08	$120.10	$120.10
Purchase #7	$85.32	7.213%	$91.4741	$91.47	$91.45	$91.50
7 purchase totals =	$723.56		$795.4787	$795.46	$795.45	$795.50