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	$232.49	4.291%	$242.4661	$242.47	$242.45	$242.50
Purchase #2	$80.59	13.805%	$91.7154	$91.72	$91.70	$91.70
Purchase #3	$89.80	10.522%	$99.2488	$99.25	$99.25	$99.20
Purchase #4	$23.51	9.422%	$25.7251	$25.73	$25.75	$25.70
Purchase #5	$105.57	11.723%	$117.946	$117.95	$117.95	$117.90
Purchase #6	$104.43	4.380%	$109.004	$109.00	$109.00	$109.00
Purchase #7	$169.53	11.786%	$189.5108	$189.51	$189.50	$189.50
7 purchase totals =	$805.92		$875.6162	$875.63	$875.60	$875.50