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	$157.82	9.318%	$172.5257	$172.53	$172.55	$172.50
Purchase #2	$84.39	8.126%	$91.2475	$91.25	$91.25	$91.20
Purchase #3	$57.94	5.795%	$61.2976	$61.30	$61.30	$61.30
Purchase #4	$20.96	4.522%	$21.9078	$21.91	$21.90	$21.90
Purchase #5	$231.97	6.270%	$246.5145	$246.51	$246.50	$246.50
Purchase #6	$31.82	7.804%	$34.3032	$34.30	$34.30	$34.30
Purchase #7	$22.60	12.851%	$25.5043	$25.50	$25.50	$25.50
7 purchase totals =	$607.50		$653.3006	$653.30	$653.30	$653.20