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	$104.66	8.845%	$113.9172	$113.92	$113.90	$113.90
Purchase #2	$140.77	4.107%	$146.5514	$146.55	$146.55	$146.60
Purchase #3	$235.87	6.131%	$250.3312	$250.33	$250.35	$250.30
Purchase #4	$60.87	11.381%	$67.7976	$67.80	$67.80	$67.80
Purchase #5	$17.66	7.301%	$18.9494	$18.95	$18.95	$18.90
Purchase #6	$201.47	5.804%	$213.1633	$213.16	$213.15	$213.20
Purchase #7	$20.47	6.667%	$21.8347	$21.83	$21.85	$21.80
7 purchase totals =	$781.77		$832.5448	$832.54	$832.55	$832.50