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	$28.29	4.413%	$29.5384	$29.54	$29.55	$29.50
Purchase #2	$95.96	8.636%	$104.2471	$104.25	$104.25	$104.20
Purchase #3	$169.32	8.821%	$184.2557	$184.26	$184.25	$184.30
Purchase #4	$85.70	9.840%	$94.1329	$94.13	$94.15	$94.10
Purchase #5	$100.42	4.241%	$104.6788	$104.68	$104.70	$104.70
Purchase #6	$112.46	13.562%	$127.7118	$127.71	$127.70	$127.70
Purchase #7	$140.71	4.576%	$147.1489	$147.15	$147.15	$147.10
7 purchase totals =	$732.86		$791.7136	$791.72	$791.75	$791.60