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	$237.56	9.790%	$260.8171	$260.82	$260.80	$260.80
Purchase #2	$47.50	6.530%	$50.6018	$50.60	$50.60	$50.60
Purchase #3	$86.40	3.668%	$89.5692	$89.57	$89.55	$89.60
Purchase #4	$151.62	10.660%	$167.7827	$167.78	$167.80	$167.80
Purchase #5	$80.90	11.815%	$90.4583	$90.46	$90.45	$90.50
Purchase #6	$238.67	11.141%	$265.2602	$265.26	$265.25	$265.30
Purchase #7	$11.43	5.312%	$12.0372	$12.04	$12.05	$12.00
7 purchase totals =	$854.08		$936.5265	$936.53	$936.50	$936.60