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	$169.34	9.389%	$185.2393	$185.24	$185.25	$185.20
Purchase #2	$44.82	9.796%	$49.2106	$49.21	$49.20	$49.20
Purchase #3	$220.97	3.294%	$228.2488	$228.25	$228.25	$228.20
Purchase #4	$66.58	10.581%	$73.6248	$73.62	$73.60	$73.60
Purchase #5	$215.89	10.461%	$238.4743	$238.47	$238.45	$238.50
Purchase #6	$213.45	9.150%	$232.9807	$232.98	$233.00	$233.00
Purchase #7	$82.83	8.385%	$89.7753	$89.78	$89.80	$89.80
7 purchase totals =	$1,013.88		$1,097.5538	$1,097.55	$1,097.55	$1,097.50