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	$45.72	10.813%	$50.6637	$50.66	$50.65	$50.70
Purchase #2	$125.83	9.300%	$137.5322	$137.53	$137.55	$137.50
Purchase #3	$115.83	13.773%	$131.7833	$131.78	$131.80	$131.80
Purchase #4	$165.71	11.264%	$184.3756	$184.38	$184.40	$184.40
Purchase #5	$87.57	4.699%	$91.6849	$91.68	$91.70	$91.70
Purchase #6	$91.39	11.618%	$102.0077	$102.01	$102.00	$102.00
Purchase #7	$210.84	4.140%	$219.5688	$219.57	$219.55	$219.60
7 purchase totals =	$842.89		$917.6162	$917.61	$917.65	$917.70