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	$162.45	12.351%	$182.5142	$182.51	$182.50	$182.50
Purchase #2	$183.61	4.537%	$191.9404	$191.94	$191.95	$191.90
Purchase #3	$107.89	11.822%	$120.6448	$120.64	$120.65	$120.60
Purchase #4	$114.98	4.651%	$120.3277	$120.33	$120.35	$120.30
Purchase #5	$214.33	12.402%	$240.9112	$240.91	$240.90	$240.90
Purchase #6	$80.92	11.327%	$90.0858	$90.09	$90.10	$90.10
Purchase #7	$140.78	3.244%	$145.3469	$145.35	$145.35	$145.30
7 purchase totals =	$1,004.96		$1,091.7710	$1,091.77	$1,091.80	$1,091.60