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	$38.98	4.862%	$40.8752	$40.88	$40.90	$40.90
Purchase #2	$160.79	6.302%	$170.923	$170.92	$170.90	$170.90
Purchase #3	$40.81	12.410%	$45.8745	$45.87	$45.85	$45.90
Purchase #4	$49.89	10.408%	$55.0826	$55.08	$55.10	$55.10
Purchase #5	$236.42	3.748%	$245.281	$245.28	$245.30	$245.30
Purchase #6	$83.59	11.862%	$93.5054	$93.51	$93.50	$93.50
Purchase #7	$141.68	11.536%	$158.0242	$158.02	$158.00	$158.00
7 purchase totals =	$752.16		$809.5659	$809.56	$809.55	$809.60