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	$40.79	7.178%	$43.7179	$43.72	$43.70	$43.70
Purchase #2	$33.80	4.476%	$35.3129	$35.31	$35.30	$35.30
Purchase #3	$11.36	4.648%	$11.888	$11.89	$11.90	$11.90
Purchase #4	$233.73	6.826%	$249.6844	$249.68	$249.70	$249.70
Purchase #5	$123.90	13.596%	$140.7454	$140.75	$140.75	$140.70
Purchase #6	$97.37	10.307%	$107.4059	$107.41	$107.40	$107.40
Purchase #7	$109.75	12.654%	$123.6378	$123.64	$123.65	$123.60
7 purchase totals =	$650.70		$712.3923	$712.40	$712.40	$712.30