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	$76.48	5.295%	$80.5296	$80.53	$80.55	$80.50
Purchase #2	$80.54	12.511%	$90.6164	$90.62	$90.60	$90.60
Purchase #3	$76.90	8.229%	$83.2281	$83.23	$83.25	$83.20
Purchase #4	$159.74	13.693%	$181.6132	$181.61	$181.60	$181.60
Purchase #5	$48.32	9.617%	$52.9669	$52.97	$52.95	$53.00
Purchase #6	$148.72	5.187%	$156.4341	$156.43	$156.45	$156.40
Purchase #7	$62.40	5.394%	$65.7659	$65.77	$65.75	$65.80
7 purchase totals =	$653.10		$711.1542	$711.16	$711.15	$711.10