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	$16.75	12.424%	$18.831	$18.83	$18.85	$18.80
Purchase #2	$177.75	10.438%	$196.3035	$196.30	$196.30	$196.30
Purchase #3	$241.73	10.407%	$266.8868	$266.89	$266.90	$266.90
Purchase #4	$174.64	6.152%	$185.3839	$185.38	$185.40	$185.40
Purchase #5	$233.34	8.478%	$253.1226	$253.12	$253.10	$253.10
Purchase #6	$117.26	12.317%	$131.7029	$131.70	$131.70	$131.70
Purchase #7	$40.75	13.653%	$46.3136	$46.31	$46.30	$46.30
7 purchase totals =	$1,002.22		$1,098.5443	$1,098.53	$1,098.55	$1,098.50