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	$238.76	6.603%	$254.5253	$254.53	$254.55	$254.50
Purchase #2	$180.81	7.333%	$194.0688	$194.07	$194.05	$194.10
Purchase #3	$78.85	12.861%	$88.9909	$88.99	$89.00	$89.00
Purchase #4	$36.59	5.196%	$38.4912	$38.49	$38.50	$38.50
Purchase #5	$131.56	9.577%	$144.1595	$144.16	$144.15	$144.20
Purchase #6	$139.88	3.858%	$145.2766	$145.28	$145.30	$145.30
Purchase #7	$18.57	12.349%	$20.8632	$20.86	$20.85	$20.90
7 purchase totals =	$825.02		$886.3755	$886.38	$886.40	$886.50