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	$152.56	12.229%	$171.2166	$171.22	$171.20	$171.20
Purchase #2	$121.32	8.683%	$131.8542	$131.85	$131.85	$131.90
Purchase #3	$187.30	12.565%	$210.8342	$210.83	$210.85	$210.80
Purchase #4	$126.38	5.805%	$133.7164	$133.72	$133.70	$133.70
Purchase #5	$244.28	11.722%	$272.9145	$272.91	$272.90	$272.90
Purchase #6	$179.43	3.414%	$185.5557	$185.56	$185.55	$185.60
Purchase #7	$96.75	8.332%	$104.8112	$104.81	$104.80	$104.80
7 purchase totals =	$1,108.02		$1,210.9028	$1,210.90	$1,210.85	$1,210.90