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	$137.30	12.657%	$154.6781	$154.68	$154.70	$154.70
Purchase #2	$139.28	3.766%	$144.5253	$144.53	$144.55	$144.50
Purchase #3	$62.29	5.781%	$65.891	$65.89	$65.90	$65.90
Purchase #4	$35.98	13.237%	$40.7427	$40.74	$40.75	$40.70
Purchase #5	$250.31	3.161%	$258.2223	$258.22	$258.20	$258.20
Purchase #6	$40.74	6.324%	$43.3164	$43.32	$43.30	$43.30
Purchase #7	$154.62	8.351%	$167.5323	$167.53	$167.55	$167.50
7 purchase totals =	$820.52		$874.9081	$874.91	$874.95	$874.80