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	$109.38	7.436%	$117.5135	$117.51	$117.50	$117.50
Purchase #2	$161.98	12.529%	$182.2745	$182.27	$182.25	$182.30
Purchase #3	$161.65	13.293%	$183.1381	$183.14	$183.15	$183.10
Purchase #4	$25.69	6.667%	$27.4028	$27.40	$27.40	$27.40
Purchase #5	$154.88	11.329%	$172.4264	$172.43	$172.45	$172.40
Purchase #6	$247.36	10.491%	$273.3105	$273.31	$273.30	$273.30
Purchase #7	$201.37	5.478%	$212.401	$212.40	$212.40	$212.40
7 purchase totals =	$1,062.31		$1,168.4668	$1,168.46	$1,168.45	$1,168.40