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	$174.52	5.126%	$183.4659	$183.47	$183.45	$183.50
Purchase #2	$247.89	8.828%	$269.7737	$269.77	$269.75	$269.80
Purchase #3	$162.44	10.530%	$179.5449	$179.54	$179.55	$179.50
Purchase #4	$42.31	10.196%	$46.6239	$46.62	$46.60	$46.60
Purchase #5	$110.44	6.377%	$117.4828	$117.48	$117.50	$117.50
Purchase #6	$19.32	9.241%	$21.1054	$21.11	$21.10	$21.10
Purchase #7	$25.71	12.124%	$28.8271	$28.83	$28.85	$28.80
7 purchase totals =	$782.63		$846.8237	$846.82	$846.80	$846.80