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	$83.91	7.396%	$90.116	$90.12	$90.10	$90.10
Purchase #2	$119.66	5.829%	$126.635	$126.64	$126.65	$126.60
Purchase #3	$37.64	13.321%	$42.654	$42.65	$42.65	$42.70
Purchase #4	$179.37	10.679%	$198.5249	$198.52	$198.50	$198.50
Purchase #5	$201.42	8.636%	$218.8146	$218.81	$218.80	$218.80
Purchase #6	$95.53	12.301%	$107.2811	$107.28	$107.30	$107.30
Purchase #7	$29.52	13.648%	$33.5489	$33.55	$33.55	$33.50
7 purchase totals =	$747.05		$817.5745	$817.57	$817.55	$817.50