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	$249.53	6.202%	$265.0059	$265.01	$265.00	$265.00
Purchase #2	$117.44	5.610%	$124.0284	$124.03	$124.05	$124.00
Purchase #3	$39.75	6.819%	$42.4606	$42.46	$42.45	$42.50
Purchase #4	$51.39	12.785%	$57.9602	$57.96	$57.95	$58.00
Purchase #5	$87.28	7.109%	$93.4847	$93.48	$93.50	$93.50
Purchase #6	$41.82	9.656%	$45.8581	$45.86	$45.85	$45.90
Purchase #7	$19.81	7.768%	$21.3488	$21.35	$21.35	$21.30
7 purchase totals =	$607.02		$650.1467	$650.15	$650.15	$650.20