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	$92.79	12.698%	$104.5725	$104.57	$104.55	$104.60
Purchase #2	$91.90	8.403%	$99.6224	$99.62	$99.60	$99.60
Purchase #3	$184.65	8.662%	$200.6444	$200.64	$200.65	$200.60
Purchase #4	$24.31	5.677%	$25.6901	$25.69	$25.70	$25.70
Purchase #5	$29.70	13.687%	$33.765	$33.77	$33.75	$33.80
Purchase #6	$243.30	10.578%	$269.0363	$269.04	$269.05	$269.00
Purchase #7	$90.38	13.212%	$102.321	$102.32	$102.30	$102.30
7 purchase totals =	$757.03		$835.6517	$835.65	$835.60	$835.60