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	$167.52	6.392%	$178.2279	$178.23	$178.25	$178.20
Purchase #2	$150.82	11.664%	$168.4116	$168.41	$168.40	$168.40
Purchase #3	$74.60	8.333%	$80.8164	$80.82	$80.80	$80.80
Purchase #4	$82.76	9.325%	$90.4774	$90.48	$90.50	$90.50
Purchase #5	$103.80	3.336%	$107.2628	$107.26	$107.25	$107.30
Purchase #6	$13.90	13.768%	$15.8138	$15.81	$15.80	$15.80
Purchase #7	$5.76	3.700%	$5.9731	$5.97	$5.95	$6.00
7 purchase totals =	$599.16		$646.9830	$646.98	$646.95	$647.00