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	$95.91	9.550%	$105.0694	$105.07	$105.05	$105.10
Purchase #2	$141.72	12.555%	$159.5129	$159.51	$159.50	$159.50
Purchase #3	$37.55	13.430%	$42.593	$42.59	$42.60	$42.60
Purchase #4	$64.87	8.611%	$70.456	$70.46	$70.45	$70.50
Purchase #5	$50.50	6.525%	$53.7951	$53.80	$53.80	$53.80
Purchase #6	$43.48	8.801%	$47.3067	$47.31	$47.30	$47.30
Purchase #7	$153.40	10.346%	$169.2708	$169.27	$169.25	$169.30
7 purchase totals =	$587.43		$648.0039	$648.01	$647.95	$648.10