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	$31.53	11.196%	$35.0601	$35.06	$35.05	$35.10
Purchase #2	$91.81	10.346%	$101.3087	$101.31	$101.30	$101.30
Purchase #3	$76.87	12.199%	$86.2474	$86.25	$86.25	$86.20
Purchase #4	$67.81	4.665%	$70.9733	$70.97	$70.95	$71.00
Purchase #5	$33.98	13.680%	$38.6285	$38.63	$38.65	$38.60
Purchase #6	$168.62	9.665%	$184.9171	$184.92	$184.90	$184.90
Purchase #7	$90.39	10.613%	$99.9831	$99.98	$100.00	$100.00
7 purchase totals =	$561.01		$617.1182	$617.12	$617.10	$617.10