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	$75.34	4.141%	$78.4598	$78.46	$78.45	$78.50
Purchase #2	$247.53	4.275%	$258.1119	$258.11	$258.10	$258.10
Purchase #3	$211.66	6.631%	$225.6952	$225.70	$225.70	$225.70
Purchase #4	$177.98	12.306%	$199.8822	$199.88	$199.90	$199.90
Purchase #5	$213.90	10.283%	$235.8953	$235.90	$235.90	$235.90
Purchase #6	$89.80	10.509%	$99.2371	$99.24	$99.25	$99.20
Purchase #7	$171.83	4.267%	$179.162	$179.16	$179.15	$179.20
7 purchase totals =	$1,188.04		$1,276.4435	$1,276.45	$1,276.45	$1,276.50