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	$18.48	11.820%	$20.6643	$20.66	$20.65	$20.70
Purchase #2	$99.52	4.566%	$104.0641	$104.06	$104.05	$104.10
Purchase #3	$168.62	6.828%	$180.1334	$180.13	$180.15	$180.10
Purchase #4	$100.79	10.742%	$111.6169	$111.62	$111.60	$111.60
Purchase #5	$211.77	12.676%	$238.614	$238.61	$238.60	$238.60
Purchase #6	$206.39	11.142%	$229.386	$229.39	$229.40	$229.40
Purchase #7	$28.39	5.211%	$29.8694	$29.87	$29.85	$29.90
7 purchase totals =	$833.96		$914.3481	$914.34	$914.30	$914.40