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	$80.46	11.300%	$89.552	$89.55	$89.55	$89.60
Purchase #2	$35.75	12.368%	$40.1716	$40.17	$40.15	$40.20
Purchase #3	$192.33	10.560%	$212.64	$212.64	$212.65	$212.60
Purchase #4	$132.57	12.125%	$148.6441	$148.64	$148.65	$148.60
Purchase #5	$239.38	3.637%	$248.0863	$248.09	$248.10	$248.10
Purchase #6	$169.62	6.397%	$180.4706	$180.47	$180.45	$180.50
Purchase #7	$149.92	7.200%	$160.7142	$160.71	$160.70	$160.70
7 purchase totals =	$1,000.03		$1,080.2788	$1,080.27	$1,080.25	$1,080.30