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	$69.31	12.264%	$77.8102	$77.81	$77.80	$77.80
Purchase #2	$46.30	7.644%	$49.8392	$49.84	$49.85	$49.80
Purchase #3	$105.98	5.252%	$111.5461	$111.55	$111.55	$111.50
Purchase #4	$70.56	3.417%	$72.971	$72.97	$72.95	$73.00
Purchase #5	$142.52	12.841%	$160.821	$160.82	$160.80	$160.80
Purchase #6	$21.30	12.796%	$24.0255	$24.03	$24.05	$24.00
Purchase #7	$51.34	5.769%	$54.3018	$54.30	$54.30	$54.30
7 purchase totals =	$507.31		$551.3148	$551.32	$551.30	$551.20