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	$38.83	4.621%	$40.6243	$40.62	$40.60	$40.60
Purchase #2	$69.93	12.409%	$78.6076	$78.61	$78.60	$78.60
Purchase #3	$242.80	9.477%	$265.8102	$265.81	$265.80	$265.80
Purchase #4	$61.43	10.693%	$67.9987	$68.00	$68.00	$68.00
Purchase #5	$152.70	10.349%	$168.5029	$168.50	$168.50	$168.50
Purchase #6	$83.77	7.673%	$90.1977	$90.20	$90.20	$90.20
Purchase #7	$135.51	5.414%	$142.8465	$142.85	$142.85	$142.80
7 purchase totals =	$784.97		$854.5879	$854.59	$854.55	$854.50