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	$240.47	9.855%	$264.1683	$264.17	$264.15	$264.20
Purchase #2	$6.45	12.810%	$7.2762	$7.28	$7.30	$7.30
Purchase #3	$240.56	10.766%	$266.4587	$266.46	$266.45	$266.50
Purchase #4	$123.42	6.553%	$131.5077	$131.51	$131.50	$131.50
Purchase #5	$83.95	5.772%	$88.7956	$88.80	$88.80	$88.80
Purchase #6	$130.61	13.591%	$148.3612	$148.36	$148.35	$148.40
Purchase #7	$63.86	7.773%	$68.8238	$68.82	$68.80	$68.80
7 purchase totals =	$889.32		$975.3915	$975.40	$975.35	$975.50