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	$109.64	12.661%	$123.5215	$123.52	$123.50	$123.50
Purchase #2	$107.37	9.340%	$117.3984	$117.40	$117.40	$117.40
Purchase #3	$154.66	11.655%	$172.6856	$172.69	$172.70	$172.70
Purchase #4	$20.89	4.362%	$21.8012	$21.80	$21.80	$21.80
Purchase #5	$172.70	9.212%	$188.6091	$188.61	$188.60	$188.60
Purchase #6	$195.63	5.569%	$206.5246	$206.52	$206.50	$206.50
Purchase #7	$165.93	11.427%	$184.8908	$184.89	$184.90	$184.90
7 purchase totals =	$926.82		$1,015.4312	$1,015.43	$1,015.40	$1,015.40