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	$56.45	9.709%	$61.9307	$61.93	$61.95	$61.90
Purchase #2	$173.61	11.823%	$194.1359	$194.14	$194.15	$194.10
Purchase #3	$173.57	12.188%	$194.7247	$194.72	$194.70	$194.70
Purchase #4	$78.99	8.759%	$85.9087	$85.91	$85.90	$85.90
Purchase #5	$235.81	8.336%	$255.4671	$255.47	$255.45	$255.50
Purchase #6	$65.40	3.834%	$67.9074	$67.91	$67.90	$67.90
Purchase #7	$60.76	13.433%	$68.9219	$68.92	$68.90	$68.90
7 purchase totals =	$844.59		$928.9964	$929.00	$928.95	$928.90