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	$16.62	3.848%	$17.2595	$17.26	$17.25	$17.30
Purchase #2	$140.58	11.702%	$157.0307	$157.03	$157.05	$157.00
Purchase #3	$129.84	11.275%	$144.4795	$144.48	$144.50	$144.50
Purchase #4	$171.65	13.319%	$194.5121	$194.51	$194.50	$194.50
Purchase #5	$178.96	9.693%	$196.3066	$196.31	$196.30	$196.30
Purchase #6	$196.75	4.675%	$205.9481	$205.95	$205.95	$205.90
Purchase #7	$80.53	9.765%	$88.3938	$88.39	$88.40	$88.40
7 purchase totals =	$914.93		$1,003.9303	$1,003.93	$1,003.95	$1,003.90