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	$18.25	3.743%	$18.9331	$18.93	$18.95	$18.90
Purchase #2	$175.56	8.690%	$190.8162	$190.82	$190.80	$190.80
Purchase #3	$95.34	5.670%	$100.7458	$100.75	$100.75	$100.70
Purchase #4	$157.58	9.692%	$172.8527	$172.85	$172.85	$172.90
Purchase #5	$27.82	11.352%	$30.9781	$30.98	$31.00	$31.00
Purchase #6	$206.90	13.215%	$234.2418	$234.24	$234.25	$234.20
Purchase #7	$67.36	9.432%	$73.7134	$73.71	$73.70	$73.70
7 purchase totals =	$748.81		$822.2811	$822.28	$822.30	$822.20