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	$19.88	8.431%	$21.5561	$21.56	$21.55	$21.60
Purchase #2	$37.68	8.433%	$40.8576	$40.86	$40.85	$40.90
Purchase #3	$241.48	12.413%	$271.4549	$271.45	$271.45	$271.50
Purchase #4	$175.27	3.826%	$181.9758	$181.98	$182.00	$182.00
Purchase #5	$174.44	6.185%	$185.2291	$185.23	$185.25	$185.20
Purchase #6	$101.67	11.304%	$113.1628	$113.16	$113.15	$113.20
Purchase #7	$48.76	6.200%	$51.7831	$51.78	$51.80	$51.80
7 purchase totals =	$799.18		$866.0194	$866.02	$866.05	$866.20