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	$137.57	13.721%	$156.446	$156.45	$156.45	$156.40
Purchase #2	$164.70	12.245%	$184.8675	$184.87	$184.85	$184.90
Purchase #3	$109.83	12.166%	$123.1919	$123.19	$123.20	$123.20
Purchase #4	$145.98	9.712%	$160.1576	$160.16	$160.15	$160.20
Purchase #5	$30.88	6.420%	$32.8625	$32.86	$32.85	$32.90
Purchase #6	$92.28	11.144%	$102.5637	$102.56	$102.55	$102.60
Purchase #7	$119.30	9.333%	$130.4343	$130.43	$130.45	$130.40
7 purchase totals =	$800.54		$890.5235	$890.52	$890.50	$890.60