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	$35.83	3.602%	$37.1206	$37.12	$37.10	$37.10
Purchase #2	$244.49	11.176%	$271.8142	$271.81	$271.80	$271.80
Purchase #3	$121.54	6.550%	$129.5009	$129.50	$129.50	$129.50
Purchase #4	$105.86	9.515%	$115.9326	$115.93	$115.95	$115.90
Purchase #5	$189.38	4.805%	$198.4797	$198.48	$198.50	$198.50
Purchase #6	$132.93	10.507%	$146.897	$146.90	$146.90	$146.90
Purchase #7	$59.47	10.280%	$65.5835	$65.58	$65.60	$65.60
7 purchase totals =	$889.50		$965.3285	$965.32	$965.35	$965.30