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	$88.96	12.318%	$99.9181	$99.92	$99.90	$99.90
Purchase #2	$227.61	10.862%	$252.333	$252.33	$252.35	$252.30
Purchase #3	$175.90	10.446%	$194.2745	$194.27	$194.25	$194.30
Purchase #4	$230.60	11.871%	$257.9745	$257.97	$257.95	$258.00
Purchase #5	$52.45	13.435%	$59.4967	$59.50	$59.50	$59.50
Purchase #6	$148.61	8.201%	$160.7975	$160.80	$160.80	$160.80
Purchase #7	$63.97	5.549%	$67.5197	$67.52	$67.50	$67.50
7 purchase totals =	$988.10		$1,092.3140	$1,092.31	$1,092.25	$1,092.30