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	$204.83	12.118%	$229.6513	$229.65	$229.65	$229.70
Purchase #2	$166.59	4.705%	$174.4281	$174.43	$174.45	$174.40
Purchase #3	$231.75	10.175%	$255.3306	$255.33	$255.35	$255.30
Purchase #4	$216.30	5.118%	$227.3702	$227.37	$227.35	$227.40
Purchase #5	$50.39	6.586%	$53.7087	$53.71	$53.70	$53.70
Purchase #6	$18.78	6.282%	$19.9598	$19.96	$19.95	$20.00
Purchase #7	$115.85	3.746%	$120.1897	$120.19	$120.20	$120.20
7 purchase totals =	$1,004.49		$1,080.6384	$1,080.64	$1,080.65	$1,080.70