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	$243.65	6.249%	$258.8757	$258.88	$258.90	$258.90
Purchase #2	$83.89	13.716%	$95.3964	$95.40	$95.40	$95.40
Purchase #3	$85.69	7.844%	$92.4115	$92.41	$92.40	$92.40
Purchase #4	$74.32	10.603%	$82.2001	$82.20	$82.20	$82.20
Purchase #5	$243.27	11.105%	$270.2851	$270.29	$270.30	$270.30
Purchase #6	$41.44	11.791%	$46.3262	$46.33	$46.35	$46.30
Purchase #7	$135.44	5.229%	$142.5222	$142.52	$142.50	$142.50
7 purchase totals =	$907.70		$988.0172	$988.03	$988.05	$988.00