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	$30.64	9.259%	$33.477	$33.48	$33.50	$33.50
Purchase #2	$164.86	9.206%	$180.037	$180.04	$180.05	$180.00
Purchase #3	$196.90	9.790%	$216.1765	$216.18	$216.20	$216.20
Purchase #4	$127.40	9.357%	$139.3208	$139.32	$139.30	$139.30
Purchase #5	$157.99	12.757%	$178.1448	$178.14	$178.15	$178.10
Purchase #6	$143.43	5.200%	$150.8884	$150.89	$150.90	$150.90
Purchase #7	$82.34	4.716%	$86.2232	$86.22	$86.20	$86.20
7 purchase totals =	$903.56		$984.2677	$984.27	$984.30	$984.20