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	$70.75	12.202%	$79.3829	$79.38	$79.40	$79.40
Purchase #2	$92.45	10.134%	$101.8189	$101.82	$101.80	$101.80
Purchase #3	$36.71	9.594%	$40.232	$40.23	$40.25	$40.20
Purchase #4	$98.32	7.550%	$105.7432	$105.74	$105.75	$105.70
Purchase #5	$112.83	6.142%	$119.76	$119.76	$119.75	$119.80
Purchase #6	$89.90	13.378%	$101.9268	$101.93	$101.95	$101.90
Purchase #7	$134.28	13.124%	$151.9029	$151.90	$151.90	$151.90
7 purchase totals =	$635.24		$700.7667	$700.76	$700.80	$700.70