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	$133.75	12.468%	$150.426	$150.43	$150.45	$150.40
Purchase #2	$149.87	4.482%	$156.5872	$156.59	$156.60	$156.60
Purchase #3	$199.69	7.825%	$215.3157	$215.32	$215.30	$215.30
Purchase #4	$158.54	10.337%	$174.9283	$174.93	$174.95	$174.90
Purchase #5	$137.34	8.738%	$149.3408	$149.34	$149.35	$149.30
Purchase #6	$20.60	4.758%	$21.5801	$21.58	$21.60	$21.60
Purchase #7	$123.94	5.808%	$131.1384	$131.14	$131.15	$131.10
7 purchase totals =	$923.73		$999.3165	$999.33	$999.40	$999.20