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	$51.95	7.108%	$55.6426	$55.64	$55.65	$55.60
Purchase #2	$117.58	12.138%	$131.8519	$131.85	$131.85	$131.90
Purchase #3	$209.49	3.326%	$216.4576	$216.46	$216.45	$216.50
Purchase #4	$88.84	10.369%	$98.0518	$98.05	$98.05	$98.10
Purchase #5	$247.61	4.263%	$258.1656	$258.17	$258.15	$258.20
Purchase #6	$50.38	11.235%	$56.0402	$56.04	$56.05	$56.00
Purchase #7	$183.46	5.290%	$193.165	$193.17	$193.15	$193.20
7 purchase totals =	$949.31		$1,009.3747	$1,009.38	$1,009.35	$1,009.50