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	$49.32	13.181%	$55.8209	$55.82	$55.80	$55.80
Purchase #2	$113.48	11.643%	$126.6925	$126.69	$126.70	$126.70
Purchase #3	$109.33	7.872%	$117.9365	$117.94	$117.95	$117.90
Purchase #4	$148.86	11.588%	$166.1099	$166.11	$166.10	$166.10
Purchase #5	$44.87	12.590%	$50.5191	$50.52	$50.50	$50.50
Purchase #6	$145.57	11.458%	$162.2494	$162.25	$162.25	$162.20
Purchase #7	$78.89	5.285%	$83.0593	$83.06	$83.05	$83.10
7 purchase totals =	$690.32		$762.3876	$762.39	$762.35	$762.30