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	$34.56	9.433%	$37.82	$37.82	$37.80	$37.80
Purchase #2	$150.78	12.853%	$170.1598	$170.16	$170.15	$170.20
Purchase #3	$242.97	12.691%	$273.8053	$273.81	$273.80	$273.80
Purchase #4	$15.92	3.354%	$16.454	$16.45	$16.45	$16.50
Purchase #5	$32.56	8.442%	$35.3087	$35.31	$35.30	$35.30
Purchase #6	$157.48	6.526%	$167.7571	$167.76	$167.75	$167.80
Purchase #7	$94.30	11.433%	$105.0813	$105.08	$105.10	$105.10
7 purchase totals =	$728.57		$806.3862	$806.39	$806.35	$806.50