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	$247.93	5.127%	$260.6414	$260.64	$260.65	$260.60
Purchase #2	$81.56	6.403%	$86.7823	$86.78	$86.80	$86.80
Purchase #3	$214.48	6.846%	$229.1633	$229.16	$229.15	$229.20
Purchase #4	$5.84	13.710%	$6.6407	$6.64	$6.65	$6.60
Purchase #5	$57.28	4.521%	$59.8696	$59.87	$59.85	$59.90
Purchase #6	$77.80	5.562%	$82.1272	$82.13	$82.15	$82.10
Purchase #7	$104.48	11.391%	$116.3813	$116.38	$116.40	$116.40
7 purchase totals =	$789.37		$841.6058	$841.60	$841.65	$841.60