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	$152.39	3.113%	$157.1339	$157.13	$157.15	$157.10
Purchase #2	$59.77	12.300%	$67.1217	$67.12	$67.10	$67.10
Purchase #3	$49.86	8.819%	$54.2572	$54.26	$54.25	$54.30
Purchase #4	$33.35	12.375%	$37.4771	$37.48	$37.50	$37.50
Purchase #5	$37.78	13.527%	$42.8905	$42.89	$42.90	$42.90
Purchase #6	$183.25	6.137%	$194.4961	$194.50	$194.50	$194.50
Purchase #7	$43.93	3.841%	$45.6174	$45.62	$45.60	$45.60
7 purchase totals =	$560.33		$598.9939	$599.00	$599.00	$599.00