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	$107.70	3.851%	$111.8475	$111.85	$111.85	$111.80
Purchase #2	$127.46	5.523%	$134.4996	$134.50	$134.50	$134.50
Purchase #3	$131.39	8.819%	$142.9773	$142.98	$143.00	$143.00
Purchase #4	$238.68	13.261%	$270.3314	$270.33	$270.35	$270.30
Purchase #5	$46.87	10.455%	$51.7703	$51.77	$51.75	$51.80
Purchase #6	$239.53	7.833%	$258.2924	$258.29	$258.30	$258.30
Purchase #7	$209.96	5.811%	$222.1608	$222.16	$222.15	$222.20
7 purchase totals =	$1,101.59		$1,191.8793	$1,191.88	$1,191.90	$1,191.90