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	$126.58	8.481%	$137.3152	$137.32	$137.30	$137.30
Purchase #2	$89.51	11.178%	$99.5154	$99.52	$99.50	$99.50
Purchase #3	$40.50	6.825%	$43.2641	$43.26	$43.25	$43.30
Purchase #4	$102.70	13.592%	$116.659	$116.66	$116.65	$116.70
Purchase #5	$146.31	11.840%	$163.6331	$163.63	$163.65	$163.60
Purchase #6	$229.56	13.151%	$259.7494	$259.75	$259.75	$259.70
Purchase #7	$32.80	11.330%	$36.5162	$36.52	$36.50	$36.50
7 purchase totals =	$767.96		$856.6524	$856.66	$856.60	$856.60