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	$52.95	12.393%	$59.5121	$59.51	$59.50	$59.50
Purchase #2	$236.51	4.694%	$247.6118	$247.61	$247.60	$247.60
Purchase #3	$123.50	13.159%	$139.7514	$139.75	$139.75	$139.80
Purchase #4	$92.87	4.300%	$96.8634	$96.86	$96.85	$96.90
Purchase #5	$115.81	8.761%	$125.9561	$125.96	$125.95	$126.00
Purchase #6	$82.48	7.114%	$88.3476	$88.35	$88.35	$88.30
Purchase #7	$143.49	6.223%	$152.4194	$152.42	$152.40	$152.40
7 purchase totals =	$847.61		$910.4618	$910.46	$910.40	$910.50