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	$23.25	3.729%	$24.117	$24.12	$24.10	$24.10
Purchase #2	$250.70	9.708%	$275.038	$275.04	$275.05	$275.00
Purchase #3	$148.29	6.615%	$158.0994	$158.10	$158.10	$158.10
Purchase #4	$120.56	8.664%	$131.0053	$131.01	$131.00	$131.00
Purchase #5	$174.42	4.348%	$182.0038	$182.00	$182.00	$182.00
Purchase #6	$65.26	6.318%	$69.3831	$69.38	$69.40	$69.40
Purchase #7	$83.84	7.419%	$90.0601	$90.06	$90.05	$90.10
7 purchase totals =	$866.32		$929.7067	$929.71	$929.70	$929.70