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	$127.85	5.376%	$134.7232	$134.72	$134.70	$134.70
Purchase #2	$91.56	9.547%	$100.3012	$100.30	$100.30	$100.30
Purchase #3	$98.26	11.485%	$109.5452	$109.55	$109.55	$109.50
Purchase #4	$120.34	9.617%	$131.9131	$131.91	$131.90	$131.90
Purchase #5	$128.58	10.525%	$142.113	$142.11	$142.10	$142.10
Purchase #6	$104.90	9.552%	$114.92	$114.92	$114.90	$114.90
Purchase #7	$122.38	3.586%	$126.7685	$126.77	$126.75	$126.80
7 purchase totals =	$793.87		$860.2842	$860.28	$860.20	$860.20