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	$113.95	12.451%	$128.1379	$128.14	$128.15	$128.10
Purchase #2	$50.75	5.658%	$53.6214	$53.62	$53.60	$53.60
Purchase #3	$78.28	3.696%	$81.1732	$81.17	$81.15	$81.20
Purchase #4	$26.28	13.743%	$29.8917	$29.89	$29.90	$29.90
Purchase #5	$42.25	7.284%	$45.3275	$45.33	$45.35	$45.30
Purchase #6	$137.46	4.218%	$143.2581	$143.26	$143.25	$143.30
Purchase #7	$52.96	4.520%	$55.3538	$55.35	$55.35	$55.40
7 purchase totals =	$501.93		$536.7636	$536.76	$536.75	$536.80