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	$57.47	9.341%	$62.8383	$62.84	$62.85	$62.80
Purchase #2	$138.99	5.611%	$146.7887	$146.79	$146.80	$146.80
Purchase #3	$82.33	11.455%	$91.7609	$91.76	$91.75	$91.80
Purchase #4	$19.43	10.767%	$21.522	$21.52	$21.50	$21.50
Purchase #5	$89.95	13.198%	$101.8216	$101.82	$101.80	$101.80
Purchase #6	$130.44	11.552%	$145.5084	$145.51	$145.50	$145.50
Purchase #7	$61.91	6.135%	$65.7082	$65.71	$65.70	$65.70
7 purchase totals =	$580.52		$635.9481	$635.95	$635.90	$635.90