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	$49.32	13.843%	$56.1474	$56.15	$56.15	$56.10
Purchase #2	$121.46	10.443%	$134.1441	$134.14	$134.15	$134.10
Purchase #3	$182.86	12.721%	$206.1216	$206.12	$206.10	$206.10
Purchase #4	$168.95	5.519%	$178.2744	$178.27	$178.25	$178.30
Purchase #5	$131.93	8.280%	$142.8538	$142.85	$142.85	$142.90
Purchase #6	$73.68	12.762%	$83.083	$83.08	$83.10	$83.10
Purchase #7	$122.48	4.477%	$127.9634	$127.96	$127.95	$128.00
7 purchase totals =	$850.68		$928.5877	$928.57	$928.55	$928.60