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	$34.79	6.116%	$36.9178	$36.92	$36.90	$36.90
Purchase #2	$57.94	12.663%	$65.2769	$65.28	$65.30	$65.30
Purchase #3	$199.98	12.121%	$224.2196	$224.22	$224.20	$224.20
Purchase #4	$53.34	13.275%	$60.4209	$60.42	$60.40	$60.40
Purchase #5	$34.50	3.152%	$35.5874	$35.59	$35.60	$35.60
Purchase #6	$130.73	10.250%	$144.1298	$144.13	$144.15	$144.10
Purchase #7	$100.74	3.161%	$103.9244	$103.92	$103.90	$103.90
7 purchase totals =	$612.02		$670.4768	$670.48	$670.45	$670.40