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	$22.31	10.253%	$24.5974	$24.60	$24.60	$24.60
Purchase #2	$211.61	10.718%	$234.2904	$234.29	$234.30	$234.30
Purchase #3	$46.34	9.436%	$50.7126	$50.71	$50.70	$50.70
Purchase #4	$152.68	13.686%	$173.5758	$173.58	$173.60	$173.60
Purchase #5	$56.73	4.365%	$59.2063	$59.21	$59.20	$59.20
Purchase #6	$99.89	9.598%	$109.4774	$109.48	$109.50	$109.50
Purchase #7	$128.60	6.745%	$137.2741	$137.27	$137.25	$137.30
7 purchase totals =	$718.16		$789.1340	$789.14	$789.15	$789.20