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	$35.29	9.138%	$38.5148	$38.51	$38.50	$38.50
Purchase #2	$148.89	13.753%	$169.3668	$169.37	$169.35	$169.40
Purchase #3	$138.98	9.281%	$151.8787	$151.88	$151.90	$151.90
Purchase #4	$23.76	3.547%	$24.6028	$24.60	$24.60	$24.60
Purchase #5	$56.65	5.138%	$59.5607	$59.56	$59.55	$59.60
Purchase #6	$9.90	3.384%	$10.235	$10.24	$10.25	$10.20
Purchase #7	$199.92	7.775%	$215.4638	$215.46	$215.45	$215.50
7 purchase totals =	$613.39		$669.6226	$669.62	$669.60	$669.70