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	$112.48	4.121%	$117.1153	$117.12	$117.10	$117.10
Purchase #2	$64.83	4.607%	$67.8167	$67.82	$67.80	$67.80
Purchase #3	$43.82	12.664%	$49.3694	$49.37	$49.35	$49.40
Purchase #4	$35.83	9.653%	$39.2887	$39.29	$39.30	$39.30
Purchase #5	$57.92	10.206%	$63.8313	$63.83	$63.85	$63.80
Purchase #6	$50.56	9.581%	$55.4042	$55.40	$55.40	$55.40
Purchase #7	$187.61	11.126%	$208.4835	$208.48	$208.50	$208.50
7 purchase totals =	$553.05		$601.3091	$601.31	$601.30	$601.30