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	$89.27	12.478%	$100.4091	$100.41	$100.40	$100.40
Purchase #2	$237.80	13.343%	$269.5297	$269.53	$269.55	$269.50
Purchase #3	$74.81	4.384%	$78.0897	$78.09	$78.10	$78.10
Purchase #4	$58.63	5.487%	$61.847	$61.85	$61.85	$61.80
Purchase #5	$42.84	5.596%	$45.2373	$45.24	$45.25	$45.20
Purchase #6	$56.25	10.453%	$62.1298	$62.13	$62.15	$62.10
Purchase #7	$51.94	10.127%	$57.2	$57.20	$57.20	$57.20
7 purchase totals =	$611.54		$674.4426	$674.45	$674.50	$674.30