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	$80.51	9.510%	$88.1665	$88.17	$88.15	$88.20
Purchase #2	$142.49	5.745%	$150.6761	$150.68	$150.70	$150.70
Purchase #3	$169.71	5.720%	$179.4174	$179.42	$179.40	$179.40
Purchase #4	$165.92	11.803%	$185.5035	$185.50	$185.50	$185.50
Purchase #5	$162.36	13.852%	$184.8501	$184.85	$184.85	$184.90
Purchase #6	$85.68	12.449%	$96.3463	$96.35	$96.35	$96.30
Purchase #7	$215.86	5.592%	$227.9309	$227.93	$227.95	$227.90
7 purchase totals =	$1,022.53		$1,112.8908	$1,112.90	$1,112.90	$1,112.90