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	$24.48	13.843%	$27.8688	$27.87	$27.85	$27.90
Purchase #2	$89.25	4.864%	$93.5911	$93.59	$93.60	$93.60
Purchase #3	$29.73	13.196%	$33.6532	$33.65	$33.65	$33.70
Purchase #4	$17.32	6.702%	$18.4808	$18.48	$18.50	$18.50
Purchase #5	$201.93	11.839%	$225.8365	$225.84	$225.85	$225.80
Purchase #6	$95.28	8.441%	$103.3226	$103.32	$103.30	$103.30
Purchase #7	$85.95	3.387%	$88.8611	$88.86	$88.85	$88.90
7 purchase totals =	$543.94		$591.6141	$591.61	$591.60	$591.70