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	$138.83	10.162%	$152.9379	$152.94	$152.95	$152.90
Purchase #2	$96.60	9.165%	$105.4534	$105.45	$105.45	$105.50
Purchase #3	$185.91	5.525%	$196.1815	$196.18	$196.20	$196.20
Purchase #4	$28.27	10.698%	$31.2943	$31.29	$31.30	$31.30
Purchase #5	$170.94	4.369%	$178.4084	$178.41	$178.40	$178.40
Purchase #6	$119.58	5.490%	$126.1449	$126.14	$126.15	$126.10
Purchase #7	$26.40	7.334%	$28.3362	$28.34	$28.35	$28.30
7 purchase totals =	$766.53		$818.7566	$818.75	$818.80	$818.70