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	$78.92	3.498%	$81.6806	$81.68	$81.70	$81.70
Purchase #2	$129.39	9.494%	$141.6743	$141.67	$141.65	$141.70
Purchase #3	$62.58	13.234%	$70.8618	$70.86	$70.85	$70.90
Purchase #4	$146.96	5.635%	$155.2412	$155.24	$155.25	$155.20
Purchase #5	$116.47	6.146%	$123.6282	$123.63	$123.65	$123.60
Purchase #6	$86.83	9.239%	$94.8522	$94.85	$94.85	$94.90
Purchase #7	$56.57	5.797%	$59.8494	$59.85	$59.85	$59.80
7 purchase totals =	$677.72		$727.7877	$727.78	$727.80	$727.80