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	$85.74	5.802%	$90.7146	$90.71	$90.70	$90.70
Purchase #2	$114.47	13.772%	$130.2348	$130.23	$130.25	$130.20
Purchase #3	$71.60	5.295%	$75.3912	$75.39	$75.40	$75.40
Purchase #4	$19.59	7.807%	$21.1194	$21.12	$21.10	$21.10
Purchase #5	$74.98	3.254%	$77.4198	$77.42	$77.40	$77.40
Purchase #6	$164.38	12.854%	$185.5094	$185.51	$185.50	$185.50
Purchase #7	$171.42	12.258%	$192.4327	$192.43	$192.45	$192.40
7 purchase totals =	$702.18		$772.8219	$772.81	$772.80	$772.70