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	$238.74	8.758%	$259.6488	$259.65	$259.65	$259.60
Purchase #2	$184.74	3.480%	$191.169	$191.17	$191.15	$191.20
Purchase #3	$42.53	5.412%	$44.8317	$44.83	$44.85	$44.80
Purchase #4	$228.86	9.618%	$250.8718	$250.87	$250.85	$250.90
Purchase #5	$86.31	4.125%	$89.8703	$89.87	$89.85	$89.90
Purchase #6	$209.88	8.843%	$228.4397	$228.44	$228.45	$228.40
Purchase #7	$183.97	11.140%	$204.4643	$204.46	$204.45	$204.50
7 purchase totals =	$1,175.03		$1,269.2956	$1,269.29	$1,269.25	$1,269.30