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	$198.89	12.778%	$224.3042	$224.30	$224.30	$224.30
Purchase #2	$245.32	11.494%	$273.5171	$273.52	$273.50	$273.50
Purchase #3	$126.50	10.286%	$139.5118	$139.51	$139.50	$139.50
Purchase #4	$145.99	11.163%	$162.2869	$162.29	$162.30	$162.30
Purchase #5	$168.56	13.311%	$190.997	$191.00	$191.00	$191.00
Purchase #6	$21.50	10.681%	$23.7964	$23.80	$23.80	$23.80
Purchase #7	$85.95	5.632%	$90.7907	$90.79	$90.80	$90.80
7 purchase totals =	$992.71		$1,105.2041	$1,105.21	$1,105.20	$1,105.20