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	$56.70	13.557%	$64.3868	$64.39	$64.40	$64.40
Purchase #2	$50.66	8.514%	$54.9732	$54.97	$54.95	$55.00
Purchase #3	$224.72	9.251%	$245.5088	$245.51	$245.50	$245.50
Purchase #4	$104.71	13.658%	$119.0113	$119.01	$119.00	$119.00
Purchase #5	$113.72	4.283%	$118.5906	$118.59	$118.60	$118.60
Purchase #6	$100.98	10.469%	$111.5516	$111.55	$111.55	$111.60
Purchase #7	$135.83	8.315%	$147.1243	$147.12	$147.10	$147.10
7 purchase totals =	$787.32		$861.1466	$861.14	$861.10	$861.20