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	$47.71	6.526%	$50.8236	$50.82	$50.80	$50.80
Purchase #2	$25.71	9.718%	$28.2085	$28.21	$28.20	$28.20
Purchase #3	$75.28	13.329%	$85.3141	$85.31	$85.30	$85.30
Purchase #4	$66.87	3.431%	$69.1643	$69.16	$69.15	$69.20
Purchase #5	$68.72	4.252%	$71.642	$71.64	$71.65	$71.60
Purchase #6	$115.38	3.813%	$119.7794	$119.78	$119.80	$119.80
Purchase #7	$126.95	3.858%	$131.8477	$131.85	$131.85	$131.80
7 purchase totals =	$526.62		$556.7796	$556.77	$556.75	$556.70