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	$95.46	13.611%	$108.4531	$108.45	$108.45	$108.50
Purchase #2	$54.95	13.621%	$62.4347	$62.43	$62.45	$62.40
Purchase #3	$185.61	11.144%	$206.2944	$206.29	$206.30	$206.30
Purchase #4	$75.93	5.415%	$80.0416	$80.04	$80.05	$80.00
Purchase #5	$244.48	12.648%	$275.4018	$275.40	$275.40	$275.40
Purchase #6	$52.87	4.345%	$55.1672	$55.17	$55.15	$55.20
Purchase #7	$122.59	13.813%	$139.5234	$139.52	$139.50	$139.50
7 purchase totals =	$831.89		$927.3162	$927.30	$927.30	$927.30