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	$34.73	6.825%	$37.1003	$37.10	$37.10	$37.10
Purchase #2	$232.93	13.692%	$264.8228	$264.82	$264.80	$264.80
Purchase #3	$12.66	5.741%	$13.3868	$13.39	$13.40	$13.40
Purchase #4	$134.37	4.843%	$140.8775	$140.88	$140.90	$140.90
Purchase #5	$11.82	9.555%	$12.9494	$12.95	$12.95	$12.90
Purchase #6	$229.93	5.379%	$242.2979	$242.30	$242.30	$242.30
Purchase #7	$146.56	4.795%	$153.5876	$153.59	$153.60	$153.60
7 purchase totals =	$803.00		$865.0223	$865.03	$865.05	$865.00