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	$49.38	6.187%	$52.4351	$52.44	$52.45	$52.40
Purchase #2	$91.43	12.741%	$103.0791	$103.08	$103.10	$103.10
Purchase #3	$233.78	10.517%	$258.3666	$258.37	$258.35	$258.40
Purchase #4	$110.84	6.197%	$117.7088	$117.71	$117.70	$117.70
Purchase #5	$183.36	7.336%	$196.8113	$196.81	$196.80	$196.80
Purchase #6	$52.30	7.870%	$56.416	$56.42	$56.40	$56.40
Purchase #7	$79.79	13.139%	$90.2736	$90.27	$90.25	$90.30
7 purchase totals =	$800.88		$875.0905	$875.10	$875.05	$875.10