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	$137.42	10.806%	$152.2696	$152.27	$152.25	$152.30
Purchase #2	$122.90	7.155%	$131.6935	$131.69	$131.70	$131.70
Purchase #3	$221.58	12.728%	$249.7827	$249.78	$249.80	$249.80
Purchase #4	$153.26	3.718%	$158.9582	$158.96	$158.95	$159.00
Purchase #5	$220.58	3.417%	$228.1172	$228.12	$228.10	$228.10
Purchase #6	$90.29	13.124%	$102.1397	$102.14	$102.15	$102.10
Purchase #7	$72.27	5.402%	$76.174	$76.17	$76.15	$76.20
7 purchase totals =	$1,018.30		$1,099.1349	$1,099.13	$1,099.10	$1,099.20