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	$133.99	7.407%	$143.9146	$143.91	$143.90	$143.90
Purchase #2	$37.82	3.434%	$39.1187	$39.12	$39.10	$39.10
Purchase #3	$30.52	9.772%	$33.5024	$33.50	$33.50	$33.50
Purchase #4	$20.32	6.490%	$21.6388	$21.64	$21.65	$21.60
Purchase #5	$79.91	13.574%	$90.757	$90.76	$90.75	$90.80
Purchase #6	$194.26	10.753%	$215.1488	$215.15	$215.15	$215.10
Purchase #7	$211.57	10.627%	$234.0535	$234.05	$234.05	$234.10
7 purchase totals =	$708.39		$778.1338	$778.13	$778.10	$778.10