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	$245.96	11.357%	$273.8937	$273.89	$273.90	$273.90
Purchase #2	$136.55	12.407%	$153.4918	$153.49	$153.50	$153.50
Purchase #3	$132.33	8.563%	$143.6614	$143.66	$143.65	$143.70
Purchase #4	$64.25	12.853%	$72.5081	$72.51	$72.50	$72.50
Purchase #5	$109.94	6.786%	$117.4005	$117.40	$117.40	$117.40
Purchase #6	$93.45	7.451%	$100.413	$100.41	$100.40	$100.40
Purchase #7	$189.68	8.150%	$205.1389	$205.14	$205.15	$205.10
7 purchase totals =	$972.16		$1,066.5074	$1,066.50	$1,066.50	$1,066.50