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	$39.62	8.837%	$43.1212	$43.12	$43.10	$43.10
Purchase #2	$244.56	3.833%	$253.934	$253.93	$253.95	$253.90
Purchase #3	$114.56	4.333%	$119.5239	$119.52	$119.50	$119.50
Purchase #4	$41.51	9.764%	$45.563	$45.56	$45.55	$45.60
Purchase #5	$54.63	11.807%	$61.0802	$61.08	$61.10	$61.10
Purchase #6	$185.69	13.181%	$210.1658	$210.17	$210.15	$210.20
Purchase #7	$6.78	7.466%	$7.2862	$7.29	$7.30	$7.30
7 purchase totals =	$687.35		$740.6743	$740.67	$740.65	$740.70