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	$86.39	3.706%	$89.5916	$89.59	$89.60	$89.60
Purchase #2	$51.86	11.650%	$57.9017	$57.90	$57.90	$57.90
Purchase #3	$149.76	4.695%	$156.7912	$156.79	$156.80	$156.80
Purchase #4	$159.55	13.728%	$181.453	$181.45	$181.45	$181.50
Purchase #5	$149.52	4.197%	$155.7954	$155.80	$155.80	$155.80
Purchase #6	$15.25	7.436%	$16.384	$16.38	$16.40	$16.40
Purchase #7	$142.62	3.801%	$148.041	$148.04	$148.05	$148.00
7 purchase totals =	$754.95		$805.9579	$805.95	$806.00	$806.00