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	$240.90	12.636%	$271.3401	$271.34	$271.35	$271.30
Purchase #2	$25.67	12.756%	$28.9445	$28.94	$28.95	$28.90
Purchase #3	$139.90	7.464%	$150.3421	$150.34	$150.35	$150.30
Purchase #4	$78.31	5.859%	$82.8982	$82.90	$82.90	$82.90
Purchase #5	$247.83	5.121%	$260.5214	$260.52	$260.50	$260.50
Purchase #6	$185.44	11.581%	$206.9158	$206.92	$206.90	$206.90
Purchase #7	$63.66	7.813%	$68.6338	$68.63	$68.65	$68.60
7 purchase totals =	$981.71		$1,069.5959	$1,069.59	$1,069.60	$1,069.40