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	$53.59	11.633%	$59.8241	$59.82	$59.80	$59.80
Purchase #2	$50.99	9.839%	$56.0069	$56.01	$56.00	$56.00
Purchase #3	$210.33	13.773%	$239.2988	$239.30	$239.30	$239.30
Purchase #4	$114.96	12.575%	$129.4162	$129.42	$129.40	$129.40
Purchase #5	$151.41	13.481%	$171.8216	$171.82	$171.80	$171.80
Purchase #6	$129.93	13.137%	$146.9989	$147.00	$147.00	$147.00
Purchase #7	$176.73	13.507%	$200.6009	$200.60	$200.60	$200.60
7 purchase totals =	$887.94		$1,003.9674	$1,003.97	$1,003.90	$1,003.90