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	$84.50	9.158%	$92.2385	$92.24	$92.25	$92.20
Purchase #2	$130.84	4.314%	$136.4844	$136.48	$136.50	$136.50
Purchase #3	$92.25	9.318%	$100.8459	$100.85	$100.85	$100.80
Purchase #4	$59.45	3.257%	$61.3863	$61.39	$61.40	$61.40
Purchase #5	$95.58	9.164%	$104.339	$104.34	$104.35	$104.30
Purchase #6	$25.88	3.710%	$26.8401	$26.84	$26.85	$26.80
Purchase #7	$123.85	12.363%	$139.1616	$139.16	$139.15	$139.20
7 purchase totals =	$612.35		$661.2958	$661.30	$661.35	$661.20