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	$39.87	6.520%	$42.4695	$42.47	$42.45	$42.50
Purchase #2	$73.69	11.609%	$82.2447	$82.24	$82.25	$82.20
Purchase #3	$6.51	6.545%	$6.9361	$6.94	$6.95	$6.90
Purchase #4	$73.38	4.652%	$76.7936	$76.79	$76.80	$76.80
Purchase #5	$229.91	5.603%	$242.7919	$242.79	$242.80	$242.80
Purchase #6	$137.47	11.847%	$153.7561	$153.76	$153.75	$153.80
Purchase #7	$134.93	11.857%	$150.9287	$150.93	$150.95	$150.90
7 purchase totals =	$695.76		$755.9206	$755.92	$755.95	$755.90