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	$90.59	9.861%	$99.5231	$99.52	$99.50	$99.50
Purchase #2	$83.90	6.841%	$89.6396	$89.64	$89.65	$89.60
Purchase #3	$228.65	4.398%	$238.706	$238.71	$238.70	$238.70
Purchase #4	$128.86	13.180%	$145.8437	$145.84	$145.85	$145.80
Purchase #5	$98.78	6.441%	$105.1424	$105.14	$105.15	$105.10
Purchase #6	$52.56	12.541%	$59.1515	$59.15	$59.15	$59.20
Purchase #7	$48.30	8.446%	$52.3794	$52.38	$52.40	$52.40
7 purchase totals =	$731.64		$790.3857	$790.38	$790.40	$790.30