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	$119.38	9.752%	$131.0219	$131.02	$131.00	$131.00
Purchase #2	$49.80	12.469%	$56.0096	$56.01	$56.00	$56.00
Purchase #3	$54.95	12.662%	$61.9078	$61.91	$61.90	$61.90
Purchase #4	$97.40	3.181%	$100.4983	$100.50	$100.50	$100.50
Purchase #5	$118.89	7.103%	$127.3348	$127.33	$127.35	$127.30
Purchase #6	$104.68	7.156%	$112.1709	$112.17	$112.15	$112.20
Purchase #7	$224.66	11.422%	$250.3207	$250.32	$250.30	$250.30
7 purchase totals =	$769.76		$839.2640	$839.26	$839.20	$839.20