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	$81.77	5.510%	$86.2755	$86.28	$86.30	$86.30
Purchase #2	$209.28	3.842%	$217.3205	$217.32	$217.30	$217.30
Purchase #3	$69.32	6.113%	$73.5575	$73.56	$73.55	$73.60
Purchase #4	$18.73	8.463%	$20.3151	$20.32	$20.30	$20.30
Purchase #5	$70.28	3.501%	$72.7405	$72.74	$72.75	$72.70
Purchase #6	$161.41	3.724%	$167.4209	$167.42	$167.40	$167.40
Purchase #7	$215.33	9.237%	$235.22	$235.22	$235.20	$235.20
7 purchase totals =	$826.12		$872.8500	$872.86	$872.80	$872.80