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	$65.77	5.560%	$69.4268	$69.43	$69.45	$69.40
Purchase #2	$175.86	6.121%	$186.6244	$186.62	$186.60	$186.60
Purchase #3	$155.84	12.765%	$175.733	$175.73	$175.75	$175.70
Purchase #4	$184.87	4.119%	$192.4848	$192.48	$192.50	$192.50
Purchase #5	$29.61	10.649%	$32.7632	$32.76	$32.75	$32.80
Purchase #6	$212.67	4.166%	$221.5298	$221.53	$221.55	$221.50
Purchase #7	$75.42	3.784%	$78.2739	$78.27	$78.25	$78.30
7 purchase totals =	$900.04		$956.8359	$956.82	$956.85	$956.80