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	$134.32	6.544%	$143.1099	$143.11	$143.10	$143.10
Purchase #2	$228.34	12.765%	$257.4876	$257.49	$257.50	$257.50
Purchase #3	$232.92	9.854%	$255.8719	$255.87	$255.85	$255.90
Purchase #4	$227.49	9.365%	$248.7944	$248.79	$248.80	$248.80
Purchase #5	$246.99	6.293%	$262.5331	$262.53	$262.55	$262.50
Purchase #6	$37.89	12.463%	$42.6122	$42.61	$42.60	$42.60
Purchase #7	$29.55	5.362%	$31.1345	$31.13	$31.15	$31.10
7 purchase totals =	$1,137.50		$1,241.5436	$1,241.53	$1,241.55	$1,241.50