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	$147.60	12.140%	$165.5186	$165.52	$165.50	$165.50
Purchase #2	$91.28	13.216%	$103.3436	$103.34	$103.35	$103.30
Purchase #3	$29.92	5.247%	$31.4899	$31.49	$31.50	$31.50
Purchase #4	$192.44	4.412%	$200.9305	$200.93	$200.95	$200.90
Purchase #5	$89.96	13.330%	$101.9517	$101.95	$101.95	$102.00
Purchase #6	$25.33	4.823%	$26.5517	$26.55	$26.55	$26.60
Purchase #7	$36.86	13.332%	$41.7742	$41.77	$41.75	$41.80
7 purchase totals =	$613.39		$671.5602	$671.55	$671.55	$671.60