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	$156.91	5.631%	$165.7456	$165.75	$165.75	$165.70
Purchase #2	$247.97	10.247%	$273.3795	$273.38	$273.40	$273.40
Purchase #3	$186.41	12.773%	$210.2201	$210.22	$210.20	$210.20
Purchase #4	$249.67	6.496%	$265.8886	$265.89	$265.90	$265.90
Purchase #5	$95.69	5.113%	$100.5826	$100.58	$100.60	$100.60
Purchase #6	$175.30	3.541%	$181.5074	$181.51	$181.50	$181.50
Purchase #7	$68.88	11.136%	$76.5505	$76.55	$76.55	$76.60
7 purchase totals =	$1,180.83		$1,273.8743	$1,273.88	$1,273.90	$1,273.90