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	$89.65	12.150%	$100.5425	$100.54	$100.55	$100.50
Purchase #2	$125.88	8.809%	$136.9688	$136.97	$136.95	$137.00
Purchase #3	$244.87	13.692%	$278.3976	$278.40	$278.40	$278.40
Purchase #4	$19.41	4.249%	$20.2347	$20.23	$20.25	$20.20
Purchase #5	$64.51	4.324%	$67.2994	$67.30	$67.30	$67.30
Purchase #6	$117.38	7.225%	$125.8607	$125.86	$125.85	$125.90
Purchase #7	$67.58	7.713%	$72.7924	$72.79	$72.80	$72.80
7 purchase totals =	$729.28		$802.0961	$802.09	$802.10	$802.10