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	$24.38	10.571%	$26.9572	$26.96	$26.95	$27.00
Purchase #2	$99.25	13.843%	$112.9892	$112.99	$113.00	$113.00
Purchase #3	$92.50	12.676%	$104.2253	$104.23	$104.25	$104.20
Purchase #4	$111.55	10.563%	$123.333	$123.33	$123.35	$123.30
Purchase #5	$183.69	4.175%	$191.3591	$191.36	$191.35	$191.40
Purchase #6	$93.29	13.135%	$105.5436	$105.54	$105.55	$105.50
Purchase #7	$34.88	8.504%	$37.8462	$37.85	$37.85	$37.80
7 purchase totals =	$639.54		$702.2536	$702.26	$702.30	$702.20