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	$24.48	11.781%	$27.364	$27.36	$27.35	$27.40
Purchase #2	$48.46	7.107%	$51.9041	$51.90	$51.90	$51.90
Purchase #3	$222.89	8.709%	$242.3015	$242.30	$242.30	$242.30
Purchase #4	$236.43	4.260%	$246.5019	$246.50	$246.50	$246.50
Purchase #5	$66.66	8.145%	$72.0895	$72.09	$72.10	$72.10
Purchase #6	$207.90	12.274%	$233.4176	$233.42	$233.40	$233.40
Purchase #7	$36.29	10.852%	$40.2282	$40.23	$40.25	$40.20
7 purchase totals =	$843.11		$913.8068	$913.80	$913.80	$913.80