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	$166.86	9.256%	$182.3046	$182.30	$182.30	$182.30
Purchase #2	$242.56	9.547%	$265.7172	$265.72	$265.70	$265.70
Purchase #3	$15.26	5.253%	$16.0616	$16.06	$16.05	$16.10
Purchase #4	$202.65	10.231%	$223.3831	$223.38	$223.40	$223.40
Purchase #5	$18.40	11.253%	$20.4706	$20.47	$20.45	$20.50
Purchase #6	$95.60	10.782%	$105.9076	$105.91	$105.90	$105.90
Purchase #7	$32.58	9.742%	$35.7539	$35.75	$35.75	$35.80
7 purchase totals =	$773.91		$849.5986	$849.59	$849.55	$849.70