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	$130.33	11.129%	$144.8344	$144.83	$144.85	$144.80
Purchase #2	$231.70	12.154%	$259.8608	$259.86	$259.85	$259.90
Purchase #3	$158.45	5.120%	$166.5626	$166.56	$166.55	$166.60
Purchase #4	$144.96	13.344%	$164.3035	$164.30	$164.30	$164.30
Purchase #5	$196.58	6.123%	$208.6166	$208.62	$208.60	$208.60
Purchase #6	$62.84	7.717%	$67.6894	$67.69	$67.70	$67.70
Purchase #7	$73.91	10.217%	$81.4614	$81.46	$81.45	$81.50
7 purchase totals =	$998.77		$1,093.3287	$1,093.32	$1,093.30	$1,093.40