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	$71.96	9.430%	$78.7458	$78.75	$78.75	$78.70
Purchase #2	$93.28	3.726%	$96.7556	$96.76	$96.75	$96.80
Purchase #3	$56.46	4.705%	$59.1164	$59.12	$59.10	$59.10
Purchase #4	$215.78	13.451%	$244.8046	$244.80	$244.80	$244.80
Purchase #5	$10.26	3.212%	$10.5896	$10.59	$10.60	$10.60
Purchase #6	$108.30	7.414%	$116.3294	$116.33	$116.35	$116.30
Purchase #7	$75.70	9.303%	$82.7424	$82.74	$82.75	$82.70
7 purchase totals =	$631.74		$689.0838	$689.09	$689.10	$689.00