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	$38.93	7.680%	$41.9198	$41.92	$41.90	$41.90
Purchase #2	$86.71	10.378%	$95.7088	$95.71	$95.70	$95.70
Purchase #3	$52.30	6.504%	$55.7016	$55.70	$55.70	$55.70
Purchase #4	$120.86	5.131%	$127.0613	$127.06	$127.05	$127.10
Purchase #5	$235.74	12.529%	$265.2759	$265.28	$265.30	$265.30
Purchase #6	$156.92	6.734%	$167.487	$167.49	$167.50	$167.50
Purchase #7	$226.64	6.388%	$241.1178	$241.12	$241.10	$241.10
7 purchase totals =	$918.10		$994.2722	$994.28	$994.25	$994.30