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	$164.31	10.412%	$181.418	$181.42	$181.40	$181.40
Purchase #2	$250.27	9.271%	$273.4725	$273.47	$273.45	$273.50
Purchase #3	$35.71	6.771%	$38.1279	$38.13	$38.15	$38.10
Purchase #4	$197.54	4.224%	$205.8841	$205.88	$205.90	$205.90
Purchase #5	$79.76	3.709%	$82.7183	$82.72	$82.70	$82.70
Purchase #6	$192.95	8.432%	$209.2195	$209.22	$209.20	$209.20
Purchase #7	$159.80	8.764%	$173.8049	$173.80	$173.80	$173.80
7 purchase totals =	$1,080.34		$1,164.6452	$1,164.64	$1,164.60	$1,164.60