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	$117.66	5.535%	$124.1725	$124.17	$124.15	$124.20
Purchase #2	$168.91	11.165%	$187.7688	$187.77	$187.75	$187.80
Purchase #3	$62.31	13.188%	$70.5274	$70.53	$70.55	$70.50
Purchase #4	$19.59	5.481%	$20.6637	$20.66	$20.65	$20.70
Purchase #5	$67.44	6.762%	$72.0003	$72.00	$72.00	$72.00
Purchase #6	$99.97	7.427%	$107.3948	$107.39	$107.40	$107.40
Purchase #7	$233.34	9.537%	$255.5936	$255.59	$255.60	$255.60
7 purchase totals =	$769.22		$838.1211	$838.11	$838.10	$838.20