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	$50.47	12.146%	$56.6001	$56.60	$56.60	$56.60
Purchase #2	$207.48	9.517%	$227.2259	$227.23	$227.25	$227.20
Purchase #3	$101.59	6.199%	$107.8876	$107.89	$107.90	$107.90
Purchase #4	$85.78	4.346%	$89.508	$89.51	$89.50	$89.50
Purchase #5	$92.32	11.436%	$102.8777	$102.88	$102.90	$102.90
Purchase #6	$41.40	7.562%	$44.5307	$44.53	$44.55	$44.50
Purchase #7	$9.73	3.740%	$10.0939	$10.09	$10.10	$10.10
7 purchase totals =	$588.77		$638.7239	$638.73	$638.80	$638.70