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	$176.81	6.843%	$188.9091	$188.91	$188.90	$188.90
Purchase #2	$62.30	7.303%	$66.8498	$66.85	$66.85	$66.80
Purchase #3	$134.89	13.845%	$153.5655	$153.57	$153.55	$153.60
Purchase #4	$40.63	7.579%	$43.7093	$43.71	$43.70	$43.70
Purchase #5	$123.29	6.847%	$131.7317	$131.73	$131.75	$131.70
Purchase #6	$232.80	4.818%	$244.0163	$244.02	$244.00	$244.00
Purchase #7	$38.68	9.320%	$42.285	$42.29	$42.30	$42.30
7 purchase totals =	$809.40		$871.0667	$871.08	$871.05	$871.00