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	$109.57	10.377%	$120.9401	$120.94	$120.95	$120.90
Purchase #2	$67.75	9.815%	$74.3997	$74.40	$74.40	$74.40
Purchase #3	$240.86	11.859%	$269.4236	$269.42	$269.40	$269.40
Purchase #4	$189.66	7.637%	$204.1443	$204.14	$204.15	$204.10
Purchase #5	$117.35	11.739%	$131.1257	$131.13	$131.15	$131.10
Purchase #6	$113.46	8.436%	$123.0315	$123.03	$123.05	$123.00
Purchase #7	$143.33	10.496%	$158.3739	$158.37	$158.35	$158.40
7 purchase totals =	$981.98		$1,081.4388	$1,081.43	$1,081.45	$1,081.30