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	$171.52	6.454%	$182.5899	$182.59	$182.60	$182.60
Purchase #2	$105.35	9.456%	$115.3119	$115.31	$115.30	$115.30
Purchase #3	$222.56	4.192%	$231.8897	$231.89	$231.90	$231.90
Purchase #4	$121.56	5.610%	$128.3795	$128.38	$128.40	$128.40
Purchase #5	$101.61	9.786%	$111.5536	$111.55	$111.55	$111.60
Purchase #6	$181.46	8.698%	$197.2434	$197.24	$197.25	$197.20
Purchase #7	$161.93	7.400%	$173.9128	$173.91	$173.90	$173.90
7 purchase totals =	$1,065.99		$1,140.8808	$1,140.87	$1,140.90	$1,140.90