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	$173.33	7.589%	$186.484	$186.48	$186.50	$186.50
Purchase #2	$34.66	11.716%	$38.7208	$38.72	$38.70	$38.70
Purchase #3	$145.58	10.534%	$160.9154	$160.92	$160.90	$160.90
Purchase #4	$74.43	5.468%	$78.4998	$78.50	$78.50	$78.50
Purchase #5	$63.89	4.337%	$66.6609	$66.66	$66.65	$66.70
Purchase #6	$214.96	13.459%	$243.8915	$243.89	$243.90	$243.90
Purchase #7	$191.93	5.755%	$202.9756	$202.98	$203.00	$203.00
7 purchase totals =	$898.78		$978.1480	$978.15	$978.15	$978.20