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	$69.70	13.414%	$79.0496	$79.05	$79.05	$79.00
Purchase #2	$29.72	4.798%	$31.146	$31.15	$31.15	$31.10
Purchase #3	$125.27	13.515%	$142.2002	$142.20	$142.20	$142.20
Purchase #4	$159.37	6.229%	$169.2972	$169.30	$169.30	$169.30
Purchase #5	$128.91	10.233%	$142.1014	$142.10	$142.10	$142.10
Purchase #6	$72.42	13.535%	$82.222	$82.22	$82.20	$82.20
Purchase #7	$193.58	8.782%	$210.5802	$210.58	$210.60	$210.60
7 purchase totals =	$778.97		$856.5966	$856.60	$856.60	$856.50