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	$21.55	3.840%	$22.3775	$22.38	$22.40	$22.40
Purchase #2	$151.72	11.366%	$168.9645	$168.96	$168.95	$169.00
Purchase #3	$225.76	3.834%	$234.4156	$234.42	$234.40	$234.40
Purchase #4	$152.50	12.210%	$171.1203	$171.12	$171.10	$171.10
Purchase #5	$6.79	3.174%	$7.0055	$7.01	$7.00	$7.00
Purchase #6	$145.95	13.822%	$166.1232	$166.12	$166.10	$166.10
Purchase #7	$191.88	10.726%	$212.461	$212.46	$212.45	$212.50
7 purchase totals =	$896.15		$982.4676	$982.47	$982.40	$982.50