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	$172.55	7.818%	$186.04	$186.04	$186.05	$186.00
Purchase #2	$16.89	8.540%	$18.3324	$18.33	$18.35	$18.30
Purchase #3	$117.91	11.669%	$131.6689	$131.67	$131.65	$131.70
Purchase #4	$23.55	6.384%	$25.0534	$25.05	$25.05	$25.10
Purchase #5	$249.76	13.111%	$282.506	$282.51	$282.50	$282.50
Purchase #6	$209.62	10.424%	$231.4708	$231.47	$231.45	$231.50
Purchase #7	$117.76	12.398%	$132.3599	$132.36	$132.35	$132.40
7 purchase totals =	$908.04		$1,007.4314	$1,007.43	$1,007.40	$1,007.50