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	$85.56	12.525%	$96.2764	$96.28	$96.30	$96.30
Purchase #2	$145.93	9.547%	$159.8619	$159.86	$159.85	$159.90
Purchase #3	$74.83	10.212%	$82.4716	$82.47	$82.45	$82.50
Purchase #4	$250.82	12.206%	$281.4351	$281.44	$281.45	$281.40
Purchase #5	$164.42	5.112%	$172.8252	$172.83	$172.85	$172.80
Purchase #6	$136.90	4.776%	$143.4383	$143.44	$143.45	$143.40
Purchase #7	$67.42	8.500%	$73.1507	$73.15	$73.15	$73.20
7 purchase totals =	$925.88		$1,009.4592	$1,009.47	$1,009.50	$1,009.50