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	$79.99	11.280%	$89.0129	$89.01	$89.00	$89.00
Purchase #2	$248.28	8.515%	$269.421	$269.42	$269.40	$269.40
Purchase #3	$246.91	4.848%	$258.8802	$258.88	$258.90	$258.90
Purchase #4	$95.55	10.297%	$105.3888	$105.39	$105.40	$105.40
Purchase #5	$31.46	4.447%	$32.859	$32.86	$32.85	$32.90
Purchase #6	$54.57	11.742%	$60.9776	$60.98	$61.00	$61.00
Purchase #7	$228.40	10.794%	$253.0535	$253.05	$253.05	$253.10
7 purchase totals =	$985.16		$1,069.5930	$1,069.59	$1,069.60	$1,069.70