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	$34.33	10.105%	$37.799	$37.80	$37.80	$37.80
Purchase #2	$225.89	5.864%	$239.1362	$239.14	$239.15	$239.10
Purchase #3	$32.91	7.387%	$35.3411	$35.34	$35.35	$35.30
Purchase #4	$190.76	11.698%	$213.0751	$213.08	$213.10	$213.10
Purchase #5	$97.79	5.773%	$103.4354	$103.44	$103.45	$103.40
Purchase #6	$95.63	4.365%	$99.8042	$99.80	$99.80	$99.80
Purchase #7	$92.25	3.180%	$95.1836	$95.18	$95.20	$95.20
7 purchase totals =	$769.56		$823.7746	$823.78	$823.85	$823.70