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	$80.37	4.534%	$84.014	$84.01	$84.00	$84.00
Purchase #2	$208.28	9.284%	$227.6167	$227.62	$227.60	$227.60
Purchase #3	$95.86	3.799%	$99.5017	$99.50	$99.50	$99.50
Purchase #4	$19.87	4.867%	$20.8371	$20.84	$20.85	$20.80
Purchase #5	$191.84	12.552%	$215.9198	$215.92	$215.90	$215.90
Purchase #6	$80.41	11.724%	$89.8373	$89.84	$89.85	$89.80
Purchase #7	$177.28	6.218%	$188.3033	$188.30	$188.30	$188.30
7 purchase totals =	$853.91		$926.0299	$926.03	$926.00	$925.90