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	$19.43	8.558%	$21.0928	$21.09	$21.10	$21.10
Purchase #2	$205.93	13.164%	$233.0386	$233.04	$233.05	$233.00
Purchase #3	$153.27	8.250%	$165.9148	$165.91	$165.90	$165.90
Purchase #4	$153.83	11.684%	$171.8035	$171.80	$171.80	$171.80
Purchase #5	$51.80	11.774%	$57.8989	$57.90	$57.90	$57.90
Purchase #6	$59.56	4.550%	$62.27	$62.27	$62.25	$62.30
Purchase #7	$162.71	5.188%	$171.1514	$171.15	$171.15	$171.20
7 purchase totals =	$806.53		$883.1700	$883.16	$883.15	$883.20