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	$61.30	6.861%	$65.5058	$65.51	$65.50	$65.50
Purchase #2	$222.49	8.598%	$241.6197	$241.62	$241.60	$241.60
Purchase #3	$91.88	8.597%	$99.7789	$99.78	$99.80	$99.80
Purchase #4	$39.90	13.222%	$45.1756	$45.18	$45.20	$45.20
Purchase #5	$231.73	5.864%	$245.3186	$245.32	$245.30	$245.30
Purchase #6	$35.25	7.271%	$37.813	$37.81	$37.80	$37.80
Purchase #7	$77.36	13.527%	$87.8245	$87.82	$87.80	$87.80
7 purchase totals =	$759.91		$823.0361	$823.04	$823.00	$823.00