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	$131.67	3.558%	$136.3548	$136.35	$136.35	$136.40
Purchase #2	$106.64	4.820%	$111.78	$111.78	$111.80	$111.80
Purchase #3	$170.86	4.433%	$178.4342	$178.43	$178.45	$178.40
Purchase #4	$93.69	10.259%	$103.3017	$103.30	$103.30	$103.30
Purchase #5	$84.54	13.465%	$95.9233	$95.92	$95.90	$95.90
Purchase #6	$64.40	6.574%	$68.6337	$68.63	$68.65	$68.60
Purchase #7	$25.75	6.296%	$27.3712	$27.37	$27.35	$27.40
7 purchase totals =	$677.55		$721.7989	$721.78	$721.80	$721.80