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	$231.64	4.508%	$242.0823	$242.08	$242.10	$242.10
Purchase #2	$23.25	5.420%	$24.5102	$24.51	$24.50	$24.50
Purchase #3	$104.82	10.772%	$116.1112	$116.11	$116.10	$116.10
Purchase #4	$209.33	10.119%	$230.5121	$230.51	$230.50	$230.50
Purchase #5	$146.66	12.411%	$164.862	$164.86	$164.85	$164.90
Purchase #6	$136.76	8.830%	$148.8359	$148.84	$148.85	$148.80
Purchase #7	$93.27	11.381%	$103.8851	$103.89	$103.90	$103.90
7 purchase totals =	$945.73		$1,030.7988	$1,030.80	$1,030.80	$1,030.80