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	$96.57	9.574%	$105.8156	$105.82	$105.80	$105.80
Purchase #2	$185.85	4.548%	$194.3025	$194.30	$194.30	$194.30
Purchase #3	$164.40	9.798%	$180.5079	$180.51	$180.50	$180.50
Purchase #4	$164.72	6.410%	$175.2786	$175.28	$175.30	$175.30
Purchase #5	$107.54	4.379%	$112.2492	$112.25	$112.25	$112.20
Purchase #6	$69.58	3.277%	$71.8601	$71.86	$71.85	$71.90
Purchase #7	$105.86	11.299%	$117.8211	$117.82	$117.80	$117.80
7 purchase totals =	$894.52		$957.8350	$957.84	$957.80	$957.80