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	$37.79	13.614%	$42.9347	$42.93	$42.95	$42.90
Purchase #2	$234.86	10.633%	$259.8327	$259.83	$259.85	$259.80
Purchase #3	$222.51	9.593%	$243.8554	$243.86	$243.85	$243.90
Purchase #4	$238.49	7.478%	$256.3243	$256.32	$256.30	$256.30
Purchase #5	$14.72	5.742%	$15.5652	$15.57	$15.55	$15.60
Purchase #6	$20.40	4.327%	$21.2827	$21.28	$21.30	$21.30
Purchase #7	$245.46	13.366%	$278.2682	$278.27	$278.25	$278.30
7 purchase totals =	$1,014.23		$1,118.0632	$1,118.06	$1,118.05	$1,118.10