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	$65.64	13.182%	$74.2927	$74.29	$74.30	$74.30
Purchase #2	$53.54	10.874%	$59.3619	$59.36	$59.35	$59.40
Purchase #3	$141.33	7.237%	$151.5581	$151.56	$151.55	$151.60
Purchase #4	$162.35	6.810%	$173.406	$173.41	$173.40	$173.40
Purchase #5	$184.29	3.199%	$190.1854	$190.19	$190.20	$190.20
Purchase #6	$129.50	8.715%	$140.7859	$140.79	$140.80	$140.80
Purchase #7	$232.85	7.652%	$250.6677	$250.67	$250.65	$250.70
7 purchase totals =	$969.50		$1,040.2577	$1,040.27	$1,040.25	$1,040.40