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	$150.49	9.198%	$164.3321	$164.33	$164.35	$164.30
Purchase #2	$174.71	12.634%	$196.7829	$196.78	$196.80	$196.80
Purchase #3	$79.96	3.601%	$82.8394	$82.84	$82.85	$82.80
Purchase #4	$230.82	9.741%	$253.3042	$253.30	$253.30	$253.30
Purchase #5	$246.49	4.245%	$256.9535	$256.95	$256.95	$257.00
Purchase #6	$140.53	11.726%	$157.0085	$157.01	$157.00	$157.00
Purchase #7	$144.59	13.277%	$163.7872	$163.79	$163.80	$163.80
7 purchase totals =	$1,167.59		$1,275.0078	$1,275.00	$1,275.05	$1,275.00