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	$42.97	7.120%	$46.0295	$46.03	$46.05	$46.00
Purchase #2	$58.50	4.402%	$61.0752	$61.08	$61.10	$61.10
Purchase #3	$41.37	4.130%	$43.0786	$43.08	$43.10	$43.10
Purchase #4	$225.89	13.476%	$256.3309	$256.33	$256.35	$256.30
Purchase #5	$67.52	4.221%	$70.37	$70.37	$70.35	$70.40
Purchase #6	$93.60	13.102%	$105.8635	$105.86	$105.85	$105.90
Purchase #7	$61.25	7.637%	$65.9277	$65.93	$65.95	$65.90
7 purchase totals =	$591.10		$648.6754	$648.68	$648.75	$648.70