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	$39.80	5.223%	$41.8788	$41.88	$41.90	$41.90
Purchase #2	$214.58	4.333%	$223.8778	$223.88	$223.90	$223.90
Purchase #3	$29.27	13.368%	$33.1828	$33.18	$33.20	$33.20
Purchase #4	$74.68	5.234%	$78.5888	$78.59	$78.60	$78.60
Purchase #5	$120.61	13.123%	$136.4377	$136.44	$136.45	$136.40
Purchase #6	$177.84	6.163%	$188.8003	$188.80	$188.80	$188.80
Purchase #7	$23.59	7.757%	$25.4199	$25.42	$25.40	$25.40
7 purchase totals =	$680.37		$728.1861	$728.19	$728.25	$728.20