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	$97.78	3.113%	$100.8239	$100.82	$100.80	$100.80
Purchase #2	$163.85	10.253%	$180.6495	$180.65	$180.65	$180.60
Purchase #3	$86.62	6.410%	$92.1723	$92.17	$92.15	$92.20
Purchase #4	$8.61	3.592%	$8.9193	$8.92	$8.90	$8.90
Purchase #5	$126.76	10.321%	$139.8429	$139.84	$139.85	$139.80
Purchase #6	$191.72	9.804%	$210.5162	$210.52	$210.50	$210.50
Purchase #7	$44.71	4.722%	$46.8212	$46.82	$46.80	$46.80
7 purchase totals =	$720.05		$779.7453	$779.74	$779.65	$779.60