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	$171.59	7.107%	$183.7849	$183.78	$183.80	$183.80
Purchase #2	$211.35	3.262%	$218.2442	$218.24	$218.25	$218.20
Purchase #3	$18.87	11.582%	$21.0555	$21.06	$21.05	$21.10
Purchase #4	$177.82	5.689%	$187.9362	$187.94	$187.95	$187.90
Purchase #5	$87.40	6.333%	$92.935	$92.94	$92.95	$92.90
Purchase #6	$54.56	8.179%	$59.0225	$59.02	$59.00	$59.00
Purchase #7	$130.28	11.809%	$145.6648	$145.66	$145.65	$145.70
7 purchase totals =	$851.87		$908.6431	$908.64	$908.65	$908.60