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	$247.35	10.733%	$273.8981	$273.90	$273.90	$273.90
Purchase #2	$128.99	10.584%	$142.6423	$142.64	$142.65	$142.60
Purchase #3	$86.41	4.532%	$90.3261	$90.33	$90.35	$90.30
Purchase #4	$247.72	5.409%	$261.1192	$261.12	$261.10	$261.10
Purchase #5	$99.40	4.272%	$103.6464	$103.65	$103.65	$103.60
Purchase #6	$38.98	4.658%	$40.7957	$40.80	$40.80	$40.80
Purchase #7	$158.89	11.604%	$177.3276	$177.33	$177.35	$177.30
7 purchase totals =	$1,007.74		$1,089.7554	$1,089.77	$1,089.80	$1,089.60