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	$85.43	5.654%	$90.2602	$90.26	$90.25	$90.30
Purchase #2	$201.56	10.111%	$221.9397	$221.94	$221.95	$221.90
Purchase #3	$37.59	8.608%	$40.8257	$40.83	$40.85	$40.80
Purchase #4	$204.60	10.384%	$225.8457	$225.85	$225.85	$225.80
Purchase #5	$25.88	3.753%	$26.8513	$26.85	$26.85	$26.90
Purchase #6	$148.58	6.205%	$157.7994	$157.80	$157.80	$157.80
Purchase #7	$16.90	9.427%	$18.4932	$18.49	$18.50	$18.50
7 purchase totals =	$720.54		$782.0152	$782.02	$782.05	$782.00