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	$120.69	10.339%	$133.1681	$133.17	$133.15	$133.20
Purchase #2	$203.54	9.209%	$222.284	$222.28	$222.30	$222.30
Purchase #3	$52.43	12.715%	$59.0965	$59.10	$59.10	$59.10
Purchase #4	$129.95	12.593%	$146.3146	$146.31	$146.30	$146.30
Purchase #5	$50.55	8.505%	$54.8493	$54.85	$54.85	$54.80
Purchase #6	$219.29	4.440%	$229.0265	$229.03	$229.05	$229.00
Purchase #7	$127.86	9.617%	$140.1563	$140.16	$140.15	$140.20
7 purchase totals =	$904.31		$984.8953	$984.90	$984.90	$984.90