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	$58.69	13.770%	$66.7716	$66.77	$66.75	$66.80
Purchase #2	$116.26	13.772%	$132.2713	$132.27	$132.25	$132.30
Purchase #3	$55.71	11.847%	$62.31	$62.31	$62.30	$62.30
Purchase #4	$65.45	9.182%	$71.4596	$71.46	$71.45	$71.50
Purchase #5	$65.38	9.807%	$71.7918	$71.79	$71.80	$71.80
Purchase #6	$51.26	9.560%	$56.1605	$56.16	$56.15	$56.20
Purchase #7	$135.26	10.266%	$149.1458	$149.15	$149.15	$149.10
7 purchase totals =	$548.01		$609.9106	$609.91	$609.85	$610.00