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	$5.32	10.694%	$5.8889	$5.89	$5.90	$5.90
Purchase #2	$70.53	10.329%	$77.815	$77.82	$77.80	$77.80
Purchase #3	$141.59	8.211%	$153.216	$153.22	$153.20	$153.20
Purchase #4	$208.93	6.507%	$222.5251	$222.53	$222.55	$222.50
Purchase #5	$155.87	11.755%	$174.1925	$174.19	$174.20	$174.20
Purchase #6	$41.29	3.555%	$42.7579	$42.76	$42.75	$42.80
Purchase #7	$71.54	11.788%	$79.9731	$79.97	$79.95	$80.00
7 purchase totals =	$695.07		$756.3685	$756.38	$756.35	$756.40