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	$86.63	6.386%	$92.1622	$92.16	$92.15	$92.20
Purchase #2	$181.82	10.428%	$200.7802	$200.78	$200.80	$200.80
Purchase #3	$27.92	5.114%	$29.3478	$29.35	$29.35	$29.30
Purchase #4	$75.78	9.817%	$83.2193	$83.22	$83.20	$83.20
Purchase #5	$89.92	11.510%	$100.2698	$100.27	$100.25	$100.30
Purchase #6	$136.97	7.285%	$146.9483	$146.95	$146.95	$146.90
Purchase #7	$249.32	7.337%	$267.6126	$267.61	$267.60	$267.60
7 purchase totals =	$848.36		$920.3402	$920.34	$920.30	$920.30