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	$132.66	4.804%	$139.033	$139.03	$139.05	$139.00
Purchase #2	$5.65	4.720%	$5.9167	$5.92	$5.90	$5.90
Purchase #3	$204.30	11.779%	$228.3645	$228.36	$228.35	$228.40
Purchase #4	$53.55	11.210%	$59.553	$59.55	$59.55	$59.60
Purchase #5	$9.91	3.493%	$10.2562	$10.26	$10.25	$10.30
Purchase #6	$57.88	6.360%	$61.5612	$61.56	$61.55	$61.60
Purchase #7	$29.83	4.188%	$31.0793	$31.08	$31.10	$31.10
7 purchase totals =	$493.78		$535.7639	$535.76	$535.75	$535.90