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	$155.38	11.805%	$173.7226	$173.72	$173.70	$173.70
Purchase #2	$59.57	10.371%	$65.748	$65.75	$65.75	$65.70
Purchase #3	$212.30	10.457%	$234.5002	$234.50	$234.50	$234.50
Purchase #4	$117.45	9.634%	$128.7651	$128.77	$128.75	$128.80
Purchase #5	$169.72	10.144%	$186.9364	$186.94	$186.95	$186.90
Purchase #6	$67.88	6.413%	$72.2331	$72.23	$72.25	$72.20
Purchase #7	$127.43	3.566%	$131.9742	$131.97	$131.95	$132.00
7 purchase totals =	$909.73		$993.8796	$993.88	$993.85	$993.80