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	$28.93	11.427%	$32.2358	$32.24	$32.25	$32.20
Purchase #2	$147.66	5.180%	$155.3088	$155.31	$155.30	$155.30
Purchase #3	$52.82	7.647%	$56.8591	$56.86	$56.85	$56.90
Purchase #4	$93.84	13.527%	$106.5337	$106.53	$106.55	$106.50
Purchase #5	$29.69	6.292%	$31.5581	$31.56	$31.55	$31.60
Purchase #6	$77.68	10.461%	$85.8061	$85.81	$85.80	$85.80
Purchase #7	$160.26	11.393%	$178.5184	$178.52	$178.50	$178.50
7 purchase totals =	$590.88		$646.8200	$646.83	$646.80	$646.80