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	$67.89	5.354%	$71.5248	$71.52	$71.50	$71.50
Purchase #2	$239.64	13.847%	$272.823	$272.82	$272.80	$272.80
Purchase #3	$127.74	9.160%	$139.441	$139.44	$139.45	$139.40
Purchase #4	$213.85	10.258%	$235.7867	$235.79	$235.80	$235.80
Purchase #5	$133.59	4.463%	$139.5521	$139.55	$139.55	$139.60
Purchase #6	$190.73	8.299%	$206.5587	$206.56	$206.55	$206.60
Purchase #7	$62.86	13.407%	$71.2876	$71.29	$71.30	$71.30
7 purchase totals =	$1,036.30		$1,136.9739	$1,136.97	$1,136.95	$1,137.00