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	$20.96	7.385%	$22.5079	$22.51	$22.50	$22.50
Purchase #2	$34.88	11.738%	$38.9742	$38.97	$38.95	$39.00
Purchase #3	$50.59	5.410%	$53.3269	$53.33	$53.35	$53.30
Purchase #4	$178.73	8.671%	$194.2277	$194.23	$194.25	$194.20
Purchase #5	$36.53	10.417%	$40.3353	$40.34	$40.35	$40.30
Purchase #6	$83.72	8.620%	$90.9367	$90.94	$90.95	$90.90
Purchase #7	$152.42	6.519%	$162.3563	$162.36	$162.35	$162.40
7 purchase totals =	$557.83		$602.6650	$602.68	$602.70	$602.60