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	$16.98	8.244%	$18.3798	$18.38	$18.40	$18.40
Purchase #2	$236.48	9.691%	$259.3973	$259.40	$259.40	$259.40
Purchase #3	$100.46	10.827%	$111.3368	$111.34	$111.35	$111.30
Purchase #4	$87.53	12.595%	$98.5544	$98.55	$98.55	$98.60
Purchase #5	$194.85	11.280%	$216.8291	$216.83	$216.85	$216.80
Purchase #6	$67.29	4.524%	$70.3342	$70.33	$70.35	$70.30
Purchase #7	$50.55	6.745%	$53.9596	$53.96	$53.95	$54.00
7 purchase totals =	$754.14		$828.7912	$828.79	$828.85	$828.80