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	$11.40	7.237%	$12.225	$12.23	$12.25	$12.20
Purchase #2	$215.52	10.534%	$238.2229	$238.22	$238.20	$238.20
Purchase #3	$78.39	7.520%	$84.2849	$84.28	$84.30	$84.30
Purchase #4	$101.90	4.488%	$106.4733	$106.47	$106.45	$106.50
Purchase #5	$20.78	9.820%	$22.8206	$22.82	$22.80	$22.80
Purchase #6	$65.43	9.750%	$71.8094	$71.81	$71.80	$71.80
Purchase #7	$79.85	12.337%	$89.7011	$89.70	$89.70	$89.70
7 purchase totals =	$573.27		$625.5372	$625.53	$625.50	$625.50