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	$13.44	13.324%	$15.2307	$15.23	$15.25	$15.20
Purchase #2	$37.38	6.238%	$39.7118	$39.71	$39.70	$39.70
Purchase #3	$215.47	10.588%	$238.284	$238.28	$238.30	$238.30
Purchase #4	$245.68	11.449%	$273.8079	$273.81	$273.80	$273.80
Purchase #5	$90.59	5.486%	$95.5598	$95.56	$95.55	$95.60
Purchase #6	$29.40	12.432%	$33.055	$33.06	$33.05	$33.10
Purchase #7	$29.92	11.547%	$33.3749	$33.37	$33.35	$33.40
7 purchase totals =	$661.88		$729.0241	$729.02	$729.00	$729.10