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	$69.55	12.552%	$78.2799	$78.28	$78.30	$78.30
Purchase #2	$57.64	6.709%	$61.5071	$61.51	$61.50	$61.50
Purchase #3	$89.65	6.512%	$95.488	$95.49	$95.50	$95.50
Purchase #4	$85.98	7.656%	$92.5626	$92.56	$92.55	$92.60
Purchase #5	$68.91	8.291%	$74.6233	$74.62	$74.60	$74.60
Purchase #6	$91.34	3.153%	$94.22	$94.22	$94.20	$94.20
Purchase #7	$232.85	4.281%	$242.8183	$242.82	$242.80	$242.80
7 purchase totals =	$695.92		$739.4992	$739.50	$739.45	$739.50