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	$28.56	4.846%	$29.944	$29.94	$29.95	$29.90
Purchase #2	$177.35	10.796%	$196.4967	$196.50	$196.50	$196.50
Purchase #3	$156.65	6.361%	$166.6145	$166.61	$166.60	$166.60
Purchase #4	$31.44	5.699%	$33.2318	$33.23	$33.25	$33.20
Purchase #5	$109.86	6.546%	$117.0514	$117.05	$117.05	$117.10
Purchase #6	$45.90	4.178%	$47.8177	$47.82	$47.80	$47.80
Purchase #7	$159.39	4.231%	$166.1338	$166.13	$166.15	$166.10
7 purchase totals =	$709.15		$757.2899	$757.28	$757.30	$757.20