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	$33.97	13.333%	$38.4992	$38.50	$38.50	$38.50
Purchase #2	$20.88	8.738%	$22.7045	$22.70	$22.70	$22.70
Purchase #3	$109.84	12.438%	$123.5019	$123.50	$123.50	$123.50
Purchase #4	$25.38	10.722%	$28.1012	$28.10	$28.10	$28.10
Purchase #5	$141.32	4.567%	$147.7741	$147.77	$147.75	$147.80
Purchase #6	$53.56	10.653%	$59.2657	$59.27	$59.25	$59.30
Purchase #7	$234.51	13.162%	$265.3762	$265.38	$265.40	$265.40
7 purchase totals =	$619.46		$685.2228	$685.22	$685.20	$685.30