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	$75.50	3.782%	$78.3554	$78.36	$78.35	$78.40
Purchase #2	$219.49	10.229%	$241.9416	$241.94	$241.95	$241.90
Purchase #3	$75.39	10.789%	$83.5238	$83.52	$83.50	$83.50
Purchase #4	$157.98	8.164%	$170.8775	$170.88	$170.90	$170.90
Purchase #5	$245.54	5.616%	$259.3295	$259.33	$259.35	$259.30
Purchase #6	$48.49	4.280%	$50.5654	$50.57	$50.55	$50.60
Purchase #7	$97.39	6.154%	$103.3834	$103.38	$103.40	$103.40
7 purchase totals =	$919.78		$987.9766	$987.98	$988.00	$988.00