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	$55.86	6.854%	$59.6886	$59.69	$59.70	$59.70
Purchase #2	$90.87	9.530%	$99.5299	$99.53	$99.55	$99.50
Purchase #3	$17.29	10.720%	$19.1435	$19.14	$19.15	$19.10
Purchase #4	$233.52	9.796%	$256.3956	$256.40	$256.40	$256.40
Purchase #5	$238.28	12.794%	$268.7655	$268.77	$268.75	$268.80
Purchase #6	$245.34	8.289%	$265.6762	$265.68	$265.70	$265.70
Purchase #7	$7.42	4.722%	$7.7704	$7.77	$7.75	$7.80
7 purchase totals =	$888.58		$976.9697	$976.98	$977.00	$977.00