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	$41.53	10.354%	$45.83	$45.83	$45.85	$45.80
Purchase #2	$74.96	12.389%	$84.2468	$84.25	$84.25	$84.20
Purchase #3	$70.53	13.584%	$80.1108	$80.11	$80.10	$80.10
Purchase #4	$171.51	10.143%	$188.9063	$188.91	$188.90	$188.90
Purchase #5	$46.79	3.663%	$48.5039	$48.50	$48.50	$48.50
Purchase #6	$192.87	4.108%	$200.7931	$200.79	$200.80	$200.80
Purchase #7	$115.40	10.716%	$127.7663	$127.77	$127.75	$127.80
7 purchase totals =	$713.59		$776.1572	$776.16	$776.15	$776.10